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Shrink a PDF so it fits an email attachment limitA scanned 28 MB document will not send. Here is how to get it under the limit, and what to do when compression is not enough.Put two screenshots side by side for a bug reportExpected vs actual, before vs after — one combined image is easier to review than two attachments. Here is the fast way to make one.Share your Wi-Fi with a QR code instead of spelling the passwordA QR code on the wall ends the “capital M, lowercase k, two sevens” ritual. How the format works, what to check, and when not to print one.Turn a column of values into a comma-separated listSpreadsheet column to IN(...) list, tags to a line, IDs to a query. The two-minute conversion that keeps coming back.chmod 755 vs 644: which permissions for files, folders, and scriptsThe two numbers cover most of what a web server needs. What each digit means, which to pick, and the cases where neither is right.Cron expressions explained with schedules you actually useFive fields, a few operators, and one famous trap. Work through real expressions — backups, business-hours checks, monthly jobs — and check the next run times.Encrypt a note before pasting it into chat or emailRecovery codes, API keys, door PINs — some text should not sit in a chat log in the clear. How to encrypt it here, and what this does and does not protect.Convert wareki years on Japanese forms without a lookup table平成5年 is which Gregorian year? Forms for resumes, applications, and registrations still ask in wareki. Boundary years trip everyone up — here is how to get them right.Copy text out of a PDF — and what to do with a scanThe PDF on your screen looks like text but will not let you select it — or it is a scan. How to tell the difference and pull the text either way.Writing your name in romaji for a formPassport applications, test registrations, airline tickets — many forms want your name in romaji. How Hepburn works, where the traps are, and how to convert kana reliably.Split one image into a grid for printing or postingA poster too big for A4, a panorama too wide for a feed, a game map to share in pieces. Grid-splitting one image into tiles solves all three.Run a fair random draw that people will acceptPicking a giveaway winner, ordering presenters, or assigning tasks — the draw itself is easy; making it believable takes a little more.Get the right dimensions for 16:9, 4:3, and other ratiosA thumbnail slot wants 16:9, your image is 3000 × 2000, and “just crop it” leaves gaps. How to compute the exact pixel dimensions that keep the ratio.Check text contrast before someone files a complaintLight gray on white looks fine on your monitor and is illegible on half of your users' phones. WCAG's AA and AAA levels are the objective check.Read a /24 address and know your network's size192.168.1.0/24 on a config page, a router asking for a subnet mask, a firewall rule mentioning /32. What CIDR notation means and how to get the full picture.Send an event as an .ics file anyone's calendar opensA date in an email gets buried; an .ics file lands on the calendar. How to make one that works in Google Calendar, Outlook, and Apple Calendar.Find which week of the year a date is in (ISO weeks)"Week 41" on a supplier schedule means nothing until you can map it to real dates. How ISO week numbers work and how to look them up.Write and read Morse code — including Japanese kanaTurn SOS or a short message into dots and dashes, and decode a Morse string back — plus the wabun codes Japan's telegraph used for kana.Read Roman numerals on buildings, movies, and clocksCopyright dates, monument years, and Super Bowl numbers use M, D, C, L, X, V, I. The rules for reading them and converting a year.Which standard deviation do you need: sample or population?Two different standard deviations come out of the same data. What the difference is, which to quote, and a worked example.Split a bill so the rounding actually adds up12,500 yen between 4 people is 3,125 each — awkward coins. How rounding up to a unit keeps the split clean and who keeps the difference.Turn a photo into ASCII art that actually readsASCII conversion throws away detail by design — which images survive the translation and how to size them.Get a PDF's table of contents out as textThe bookmarks panel in a PDF reader is a ready-made outline — if the file has one. How to list it with page numbers and copy it.What actually makes a password strongLength beats clever substitutions, and every password-strength meter is an estimate. What the checks measure and how to read the verdict.Compare two drafts word by word instead of line by lineA one-word edit inside a long paragraph is invisible in a line diff. Word-level comparison shows exactly which words changed.Diff two JSON configs to find what actually changedEnvironment configs and API responses drift apart subtly. A structural JSON diff lists added, removed, and changed paths.Extract readable text out of an HTML page or emailView-source dumps and HTML emails are unreadable. Strip the markup and keep the text — with links listed separately if needed.Write a large number in English words (and Japanese)Checks, contracts, and formal writing spell numbers out. Convert any whole number to words in both languages at once.Convert prices between net and gross with consumption taxA quote is tax-exclusive but the invoice must show tax-inclusive. Convert both directions at 10%, 8%, or any rate.Check your user agent and browser details for a bug reportSupport teams ask for your browser and screen details. Get them all in one view — nothing is sent anywhere.Make a JAN/EAN-13 barcode image for a product codeGenerate the striped barcode from a 12- or 13-digit JAN/EAN number and save it as PNG.Check an image's dimensions and format before uploadingA form rejects your image and you don't know why. Check the real dimensions, format, file size, and aspect ratio in one click.Turn an API response into TypeScript typesYou have a real JSON payload and an empty .ts file. Infer a first draft of interfaces instead of writing field names by hand.Shrink SVG files exported from design toolsEditor-exported SVGs carry comments and metadata that inflate the file. Strip them before shipping icons on the web.Write a CSS gradient without memorizing the syntaxlinear-gradient(135deg, ...) is easy to mistype by hand. Set stops on a preview and copy the exact CSS.Turn spreadsheet rows into a Markdown tablePasting tab-separated rows into a README breaks the table. Convert the rows to aligned Markdown pipes in one step.Estimate a monthly loan payment before you applyA 300,000 loan at 1.5% over 3 years — what is the monthly payment, and how much interest do you pay in total?Find the cheapest option by price per unit500 g for 398 yen or 750 g for 550 yen? The bigger bag is not always the deal. Compare per-unit prices directly.Straighten a tilted photo without losing the edgesA horizon that is 3° off ruins a good shot. Rotate by the exact angle and choose whether to keep the whole image or fill the frame.Warm up mouse aim and track your reactionThirty seconds of target clicks before a match. Measure hits, accuracy, and average reaction to see if your hand is awake.Estimate savings growth with compoundingWhat a starting amount plus monthly contributions becomes over years at a given rate — and what the number does and does not mean.Work out a sale price from a percent off“20% off ¥3,980” is easy to misjudge in your head. Get the exact sale price — or work backwards from a tag to the original price.Calculate BMI and read what the band meansHeight and weight to a BMI, its WHO category, and the weight range that would be “normal” at that height — plus where the number stops being useful.Add up work hours from clock timesHow long between 9:15 and 17:45, and what is the weekly total of daily entries? Clock-time arithmetic without a spreadsheet.Rasterize an SVG for places that need pixelsSNS previews, slide decks, and older apps often refuse SVG. Convert it to PNG at a chosen scale — and know what rasterizing gives up.Share your contact details as a QR codeA QR that adds you to someone’s contacts is faster than spelling an address aloud. What goes in the card and what scanning actually does.Watermark photos before sharing themA corner credit or a tiled mark across the image — how to place a readable watermark without wrecking the photo.Find which key code a key actually firesevent.key and event.code are not the same thing, and neither is stable across layouts. See exactly what your browser reports for each key.Split a restaurant bill with a tipWork out the tip, the total, and each person's share — and why the rounded shares collect a few cents extra.Compare hourly pay with a salary offerTurn a ¥1,600 shift or a $25/hour listing into the same units so offers can be compared honestly.Work out a weighted gradeQuizzes, homework, and finals rarely weigh the same. Combine them correctly, then ask what the remaining work needs.Check your typing speedA fixed passage, a timer that starts on your first keystroke, and the WPM conventions behind the number.Practice with a metronomeSet a BPM or tap it out, hear a steady click, and use the accent to feel the bar line.Make a Code 128 barcodeEncode asset tags, ticket IDs, or serial strings into a scannable barcode — and know when EAN is the wrong tool.Hide part of a photo before sharingNames, addresses, and faces leak through screenshots and photos. Mark the regions, choose black or mosaic, and keep the original.Tune a CSS box shadowOffset, blur, spread, color, and inset each change a different thing. See what each value does on a live card.Compare two listsFind which names, emails, or keywords appear in both lists — and which are missing from either side.Plan sleep around cyclesWake up at a cycle boundary instead of mid-cycle: pick a fixed wake time, then count back 90-minute blocks plus the time you need to fall asleep.Convert px to rem (and back)rem scales with the reader’s root font size — converting px values makes layouts respect browser zoom and user settings.Find and replace across a textRename a term everywhere it appears, strip a prefix from every line, or reshape patterns with a regular expression.Make a round avatar imageCrop a square from the center and clip it to a circle, or just soften the corners — the result needs transparency, so it is PNG only.Scale a recipe up or downFour servings becoming seven, or a halved batch: scale every ingredient quantity at once instead of doing each line in your head.Set a delay to the tempoEchoes that land on the beat need milliseconds, not knob positions — convert BPM into note-length delay times.Solve a proportion“200g for 300 yen — how much for 500g?” Cross-multiplication answers it: fill three of the four positions.Find the words you repeat too oftenEvery writer has crutch words. A frequency count makes them visible — and tells you where to prune.Time an activity and keep lap splitsA stopwatch is only half the job — the lap table is what tells you which stretch was slow.Work out your GPA before the transcript arrivesGrades and credits → a 4.0-scale GPA, so you know where you stand before the official number.Pick colors that go togetherOne base color, five harmonies — a starting palette for a button, a chart, or a slide.Plan your race pace from a recent runA 52-minute 10k is a 5:12/km pace — knowing the number changes how you start the race.Convert a note name to its frequencyA4 is 440 Hz — but what about the C two octaves down, or the F# your synth is playing?Check if a number's check digit is rightLuhn's mod-10 formula catches typos in card-number-shaped test data — before your QA form rejects it.Have a long text read aloudProofreading by ear catches what the eye skips — your browser already has the voices.Read a resistor's color bandsThe bands on a resistor are its value written in color — once the order clicks, you never need to guess.Solve a circuit with Ohm's lawKnow any two of V, I, R, P and the rest follow — the four equations are really one.Train in the right heart-rate zoneZone 2 gets all the attention for a reason — but you need the numbers first.Identify a strange characterAn invisible character broke your CSV or your regex. The code point tells you what it actually is.Estimate how long a download will take4 GB at 100 Mbps is not 40 seconds — the bits-versus-bytes factor of eight surprises everyone once.Measure your reaction timeMedian human visual reaction is around 250 ms — see where you land.Run work/rest intervals hands-freeTabata, HIIT, or study sprints — set the two intervals once and let the beeps drive.Check an IBAN before using itA mistyped IBAN bounces a transfer days later. The mod-97 check catches typos in a second.Estimate how many calories you burn each dayGet a resting and daily calorie-burn estimate from body stats and activity level — and know how far to trust it.Work out what a drive will cost in fuelTurn trip distance, your car's fuel economy, and the pump price into a fuel budget and a per-person split.Estimate what an appliance costs to runTurn watts, hours, and your kWh rate into a running-cost figure — for one device or a comparison.Roll dice for a tabletop gameRoll standard and unusual dice — 2d6+3, d20 checks, d100 percentiles — on screen.Find and fix mixed line endingsSee how many LF, CRLF, and lone CR endings a text has, then convert everything to one style.Match a color you saw in an imageClick a screenshot, logo, or photo to get the exact hex and RGB value at that pixel.Work out a GCD or LCMReduce fractions and find when repeating cycles coincide — the two jobs GCD and LCM solve.Find a song's tempo by tappingTap along with music for a few seconds and read the beats-per-minute average.Factor a number into primesEvery integer splits into one unique set of prime factors. Get that factorization, the divisor count, and the divisor list for any number up to 10¹⁵.Add fractions and get the simplified answer3/4 + 5/8 by hand means common denominators and simplifying. Enter both fractions and read the reduced answer, mixed number, and decimal.Solve a quadratic with the formulaEnter a, b, c from ax² + bx + c = 0 to get both roots — or the complex pair — plus the discriminant and vertex.Convert GPS coordinates between formatsOne device reports 35.681236, another wants 35° 40′ 52″ N. Convert latitude and longitude both ways.Strip tracking parameters from a linkShared URLs carry utm_*, fbclid, and friends that report your click. Remove them before you repost or save the link.Write meta and OG tags for a pageSearch results read title and description; social shares read Open Graph. Generate the whole block to paste into a head.Spell a name clearly on the phoneM for Mike, S for Sierra. The NATO alphabet turns a name or code into words that survive a bad connection.Keep a running count without losing trackVisitors at the door, sets at the gym, stock on a shelf — a named tally keeps each count separate and saved.Turn hiragana into katakana for a furigana fieldJapanese forms ask for your name's reading in a specific script — usually katakana. Here is the quick conversion, plus what to check before pasting.Compare apartment sizes given in m², tsubo, or tatamiOne listing says 62 m², the next says 18 jo, the land is in tsubo. Convert them to one unit before deciding which is bigger.Mask office noise with white, pink, or brown noiseA steady hiss is easier for the brain to ignore than voices or footsteps. Which noise color masks what, and how loud is enough.Check left and right speakers with a test toneNew headphones on backwards? One earbud dead? A tone sent to one channel at a time settles it in seconds.Plan a league schedule where everyone plays everyoneSix friends, one game, one evening a week. The round-robin schedule makes sure every pairing happens exactly once.Find where a delayed email spent its timeA message arrived hours late, or vanished. The Received headers record every server it passed through — and when.How many pixels does an A4 print need?300 DPI is the usual print target — but how many pixels is that for the paper size? The conversion is one formula.Pick a call time that works across time zonesTokyo, London, New York — a 15:00 in one place is midnight in another. See the same instant in every zone before proposing.Write a number in kanji — standard and formal daijiA form or contract wants 12,345 written as kanji — or a legacy document has 壱万弐千参百四拾五 you need as digits. Convert both ways.Retab code between tabs and spacesPasted code breaks the file's indent convention — a review tool rejects mixed indentation. Convert the leading whitespace in one pass.Pull every link out of a block of textA meeting note or log is full of URLs and addresses scattered in prose. Get one clean, deduplicated list instead of hunting line by line.Set a price from a target margin"30% margin on a 700 cost" is not 910 — margin and markup divide by different bases. Get the actual price and profit.Solve a triangle from three measurementsYou know two boards and the angle between them, or three sides of a frame. Find the missing lengths and angles — and the area — before cutting.Convert frames to timecode at your frame rateAn editor says "frame 10800" while your player shows a time. Convert both directions — and see why 29.97 fps timecode drifts from the clock.Compare two screens' sharpness with PPIA 27" 1440p monitor and a 24" 1080p one look similar on a shelf — but the pixel density differs. Put numbers on sharpness before buying.Draw a knockout tournament bracketSeven players, one afternoon, single elimination — who plays whom? Generate a seeded bracket with byes placed correctly, or a shuffled draw.Pull matching lines out of a long textLogs, exports, pasted lists — keep only the lines that matter, or strip the noise out, without a script.Put line numbers on a text — or take them offNumber lines before pasting into a ticket or doc, or strip existing prefixes from copied output.Find the hidden characters breaking pasted textA no-break space or zero-width character can break matching, sorting, and parsing. Make them visible to see what you actually have.Write text as Unicode escapes for source codeProperties files, JSON strings, HTML entities — convert non-ASCII text to escapes and read escapes back.Fix subtitles that run early or lateWhen subtitles drift from the audio by a constant amount, shifting every timestamp fixes them in one pass.Turn clock times into decimal hours for a timesheet7 hours 45 minutes is 7.75 hours — the conversion payroll and timesheet forms expect.Find the 100th day and other milestone datesWhen is the 100th day since a start date? The 1,000th? List milestones and year anniversaries in one pass.Convert a dog's or cat's age to human yearsThe "multiply by seven" rule is wrong — use the size-aware estimate vets actually quote.Add the same text to the start or end of every lineTurn a pasted list into bullet items, quoted CSV values, or commented-out code in one pass.Verify a webhook HMAC signature locallyRecompute the expected signature for a payload and secret, and compare it with the header you received.Turn pasted HTML into MarkdownConvert a copied article fragment or exported markup into Markdown you can paste into docs, notes, or a CMS.Estimate how long a script takes to read aloudFind out whether your talk fits the slot before you rehearse — by words per minute or characters per minute.Convert a shoe size between JP, US, UK, and EUBuying shoes from an overseas shop or brand? Translate the listed size into the system you know.Check the moon phase for a dateFull moon for a photo shoot, a dark night for stargazing, or just curiosity — look up the phase and what comes next.Remove a solid-color background from an imageKey out a flat background — a logo on white, a sticker on green — and save a transparent PNG.Split a PDF into separate filesTurn one long PDF into per-page files — or fixed-size chunks — delivered together as a ZIP.Shuffle a list fairlyRandomize a line-based list — presentation order, draft picks, or a playlist — with an unbiased shuffle.Sort version numbers correctlyOrder release tags and build versions the way SemVer expects — where 1.10.0 really is newer than 1.9.0.Convert a ring size between countriesTranslate between Japan's 号 sizes, US numbers, UK letters, EU sizes, and a ruler measurement in millimetres.Estimate your one-rep maxWork out a safe single-rep maximum from a set you actually lifted — no attempt needed.Find a zodiac sign and eto animalLook up both the Western zodiac sign and the Japanese eto (十二支) animal from a birth date.Trim white edges off a scanRemove the uniform border around a scanned document, letterboxed screenshot, or padded image without picking crop corners.Print two PDF pages on one sheetLay out a PDF 2-up or 4-up on A4 or Letter paper — handouts, drafts, and paper-saving prints.Measure your clicks per secondCount clicks inside a 3, 5, or 10 second window for a quick CPS score — with an honest read on what the number means.Fix a text file that opens as garbage charactersA .csv or .txt that shows mojibake was saved in a different encoding than your editor expects. Re-decode it as the right charset and keep a clean UTF-8 copy.Find the date of the third Tuesday of a monthRecurring meetings run on rules like “second Monday” and “last Friday” — turn the rule into an actual calendar date.Decode a Caesar cipher (and ROT13)A puzzle, spoiler tag, or geocache used a letter-shift cipher. Decode it with the right shift — or try all 25 at once when you do not know it.Make bingo cards for a party or classStandard 75-ball cards, or cards built from your own words — team names, vocabulary, inside jokes. Generate one PNG per player and print.Count permutations and combinationsHow many ways to pick a committee, draw cards, or assign ranks — nPr, nCr, and nHr computed as exact integers.Make a placeholder image without an external serviceMockups and HTML samples need image files of a known size. Generate a labeled rectangle locally instead of hotlinking a placeholder service.Check whether a design reads under color blindnessAbout 1 in 12 men has some color vision difference. Preview your image, chart, or UI under the three main types before publishing.Check whether an ISBN is typed correctlyA mistyped ISBN silently finds the wrong book or none at all. Verify the check digit and convert between ISBN-10 and ISBN-13 before importing or cataloging.Style text for a social profile or postInstagram bios, X posts, Discord names — places with no bold button still show styled text. Unicode lookalike letters make it work.Write a text banner in ASCII artA plain-text heading that survives code review, terminals and README files — rendered from letters themselves, not an image.Spot the difference between two screenshotsA pixel diff answers 'what changed' between two versions of an image — a UI regression check, a before/after retouch, a doctored capture.Grab a single frame from a video as an imageA thumbnail for a listing, a still for a slide, proof of a moment — the frame comes straight off the local file at native resolution.Cut a clip out of an audio fileKeep just the verse, the quote, the sound — set a start and end and export the segment as a WAV that any editor accepts.Make a word search puzzle from your own wordsClass vocabulary, party icebreakers, holiday words — type the list and get a letter grid to print, with the words hidden inside.Generate sample data for a demo or test fixtureA table to screenshot, rows to seed a dev database, fixtures for a parser — fictional values that are safe to commit and share.Read an IPv6 addressLong hex, a :: gap, maybe a %zone suffix — expand it, compress it canonically, and see what kind of address it actually is.Convert an internationalized domain to Punycode日本語.jp or münchen.de — DNS only speaks ASCII, so unicode labels travel as xn-- strings. See the real name behind the encoding.See text as binary, hex, or octal bytesWhat does あ actually become on the wire? UTF-8 bytes shown as 0s and 1s, hex pairs, or octal — and digit strings decoded back.Convert subtitles between SRT and WebVTTA player wants .vtt, an editor exports .srt — the cues are the same, only the timestamps and header differ.Minify HTML before shipping itIndented, commented source is for humans. The shipped copy can drop the whitespace and commentary without changing what renders.Publish Markdown as HTMLNotes and docs live in Markdown; the web wants HTML. Convert a .md source to markup you can paste into a CMS or a page template.Make a meme from your own photoA screenshot, a pet photo, a reaction shot — add the classic two-line caption and get a watermark-free PNG without handing the image to anyone.Frame a screenshot in a browser mockupA raw screenshot pasted into a slide looks unfinished. Wrap it in a clean browser-window frame with margin and it reads as a product shot.Turn a set of images into an animated GIFA sequence of screenshots, a step-by-step process, a few photos stitched together — encode them into a looping GIF locally, no service needed.Check your microphone level before a call"Can you hear me?" — test the mic locally: a live RMS meter in dB, a peak readout, and a 5-second peak test. Audio never leaves the browser.Make a word cloud from pasted textSurvey responses, meeting notes, a chapter draft — a frequency cloud makes the dominant themes visible at a glance, downloadable as a PNG.Check how readable your English text isDocs, emails, landing copy — Flesch Reading Ease and Flesch–Kincaid grade level give a quick number to aim at before you ship the text.Tag a link so analytics can attribute the visitA newsletter, a social post, a QR code — without utm parameters the traffic lands in "direct". Build the tagged URL correctly instead of hand-editing the query string.Write a .gitignore without remembering every rulenode_modules, __pycache__, .DS_Store, target/ — combine the standard sections for your stack into one file instead of copying fragments from old projects.Write a sitemap.xml from a URL listA small static site does not need a crawler — paste the URLs you actually have and get a valid XML sitemap with the optional fields filled in.Turn an XML document into JSONAn API response, a config file, an old RSS feed — when the downstream code wants JSON, convert the structure instead of re-mapping fields by hand.Check what a file really isThe extension says .png, but is it? The first bytes of a file declare its real format — read them locally and compare against the name.Compare a dollar amount across yearsGrandpa's $5,000 salary, a 1990s price tag, an old contract amount — CPI-U annual averages translate between years so the numbers are comparable.Get a fresh Sudoku puzzle to solveA commute puzzle, a classroom handout, a printout for the fridge — generate a grid with a verified unique solution at three difficulty levels.Print a clean calendar for any monthA wall calendar for the kitchen, a planning sheet for a project month, a handout — one month per page, no account, no template download.Check a photo's EXIF data before sharing itPhone photos can carry the exact location where they were taken. Check what a JPG actually contains before posting or sending it.Print graph paper when the notebook runs outNeed 5 mm squares for math homework or an isometric grid for a sketch? Generate the exact ruling and print it — no store run.Convert audio to WAV for editing or compatibilitySome editors, old hardware, and voice tools only accept WAV. Decode any audio file your browser can play and save it as uncompressed PCM.Record a voice memo without installing an appA quick interview, a lecture, a melody idea — the browser's microphone is enough for a take you can replay and keep.Look inside a ZIP before you open itAn unexpected archive attachment is worth a look before extraction. List the entries and pull out just the files you actually need.Sign a test JWT for local developmentYour API expects a signed token but the auth server is not running. Build an HS256 JWT locally with the claims you need.Generate compact IDs for fixtures and testingSeed data, test fixtures, and shareable links all need IDs that are short, URL-safe, and unlikely to collide.Convert a YAML config to JSON (and back)A CI pipeline wants YAML, your script wants JSON. Convert config files between the two without installing a toolchain.Sketch a JSON Schema from a real payloadWriting a schema by hand means guessing at your own data. Infer a draft 2020-12 schema from the JSON you actually have, then tighten it.Look up what an HTTP status code meansA webhook returned 422, nginx logged a 499, the CDN says 520. Find the code's meaning and the typical cause without a spec deep-dive.Split a long post into numbered partsA 4,000-character post won't fit a 500-character limit. Split it at word boundaries with part numbers that survive the cut.Write a Russian name in Latin lettersForms, tickets, and citations all want Cyrillic names in Latin letters — and the right answer depends on which mapping they follow.Estimate how much paint a room needsBuying a can too few means a second trip mid-job; too many is money on a shelf. Get the litres from the room's dimensions before you shop.Write a simple invoice as a freelancerA client needs a PDF invoice with line items, tax, and a total — not an accounting subscription. Build one and print it to PDF.Work out an invoice due dateNet 30 from the 14th, or end of next month + 5 — payment terms are date math with conventions attached.Turn plain text into a PDF for sharingNotes, a README excerpt, a plain-language contract — sometimes the deliverable is a PDF, and the source is just text.Work out the odds of a dice rollDoes the party hit on 4d6 ≥ 14? Exact probabilities for any NdS roll — no simulation noise, no mental arithmetic.Time a chess game on one deviceA physical clock is one more thing to carry. Presets from bullet to classical plus increments turn a phone into the clock.Make a printable maze puzzleA party favour, a kids' worksheet, a bored-afternoon diversion — a fresh maze at any size, with the solution on demand.Play Minesweeper without installing anythingThe classic logic game in a tab — three difficulties, first click always safe, nothing to download.Find the MIME type for a file extensionA download comes back as application/octet-stream, or an upload form rejects your file. Here is how to find the right Content-Type value fast.Work out what an HTTP header doesA header name shows up in a curl trace or a bug report — what does it actually control, and is it request-side or response-side?Inspect a file's bytes with a hex dumpIs it really a PNG? Where does the text change encoding? A hex dump answers questions the file's name cannot.Drop an SVG file into a React componentDesign tools export SVG with HTML-invalid attributes. Here is the fast way to turn that markup into a JSX component that actually compiles.Write and test a robots.txtBlock staging from crawlers, keep /private out of Google, or verify a path is allowed — without memorizing the rule syntax.Load CSV rows into a databaseYou have a spreadsheet export and need INSERT statements to seed a table. Here is the quick path that handles quoting and NULLs properly.Pick colors in OKLCH for better palettesHSL lies about lightness — two '50%' colors can look wildly different. OKLCH fixes that. Here is how to convert your colors and read the numbers.Decode a UUID you found in a log or URLThat 36-character string encodes a version, sometimes a timestamp, sometimes a MAC. Here is how to read what kind of identifier you are holding.Make a signing key pair for JWTs or APIsYou need an RSA or EC key pair to sign tokens in a dev environment — here is the browser-local way that does not touch openssl or a server.Type arrows and symbols your keyboard lacks→, ±, §, ⌘ — the characters documents need but keyboards omit. Search, click, paste.Pull just the columns you need out of a CSVThe export has 30 columns and you want three. Keep or drop them with a selector — quoting and commas inside fields handled correctly.Add a table of contents to a Markdown docA long README needs navigation. Generate a nested TOC with GitHub-style anchors — and update it when headings change.Check text for spoofed look-alike lettersIs that 'amazon' link really amazon? Cyrillic а and Greek ο render identically to Latin letters. Scan for them before clicking.Get every frame out of an animated GIFYou need one still from an animated GIF — for a thumbnail, an edit, or documentation. Here is how to split it into PNGs correctly.Turn a video clip into a shareable GIFShort screen captures and clips become looping GIFs for docs and chats — no upload to a converter site.Record your screen without an uploadA screencast for a colleague or a bug video — captured and saved in the browser, no account and no cloud.Turn a photo into a printable coloring pageKids' photos, pet pictures, landmarks — edge detection turns them into line art you can print and color.Print a PDF as a folded bookletZines, manuals, event programs: re-order pages so two land on each sheet side, fold the stack, and the page order comes out right.Trim white margins off PDF pagesScans and print-ready PDFs arrive with fat margins. Crop them down so the content fills the view — reversibly.Work out how many tiles to buyTiles sell by the box or piece — and breakage eats the surplus. Get the count plus the waste allowance in one pass.Estimate concrete for a slab or post holesHow many bags for a shed slab or a fence line of post holes? Volume plus the yield printed on your bag.Pick a resistor for an LEDLEDs burn out without a current limiter. R=(Vs−Vf)/I gives the value — then round to the E24 shelf and check the wattage.Find sunrise and sunset for any place and dateGolden-hour photos, hike timing, prayer and workday schedules — get the sun times for coordinates without a lookup site.Play 2048 — rules and strategySlide, merge, repeat. The rules fit in a sentence; the strategy for actually reaching 2048 takes a little more.Rename variables across naming stylesA database column named user_name has to become userName in code, or the reverse. Paste the whole list and convert it in one pass.Turn a curl command into fetch() codeThe API docs give you a curl example; your project wants JavaScript. Convert the command instead of retyping every header and body field.Figure out which CSS rule winsTwo selectors target the same element and the wrong style is winning. Score both before you add another !important.Re-indent pasted HTML before reading itA minified dump, a copied template, a CMS snippet — one flat line of markup is unreadable. Re-indent it first.Find hidden characters in pasted textThe code won't compile, the URL won't match, the diff shows nothing — invisible characters are the classic suspect. Scan the text and see exactly where they are.Come up with a username when yours is takenEvery service says your usual name is taken. Generate a batch of plausible candidates instead of typing random letters.Fix quote marks in pasted textThe document wants curly typographic quotes but the paste brought straight " marks — or the reverse. Convert the whole text at once.Work out the volume of a tank, box, or containerHow much water does the tank hold? How much soil for the planter? Enter the dimensions and get the volume in litres and cubic units.Combine resistors to hit a target valueThe circuit wants 3.4 kΩ but the kit only has standard values. Two resistors in parallel or series get you there — find which pair.Size an air conditioner for a roomToo small and it runs flat out; too big and it short-cycles into clammy air. Get a first BTU estimate before shopping.Estimate how long a battery will lastA 2,000 mAh pack powering a sensor that draws 40 mA — will it survive the weekend? Capacity ÷ load, adjusted for efficiency and duty.Check when clocks change in a time zoneThe meeting invite says 9 AM New York — but is that EDT or EST this year? Check the exact change dates before scheduling.Find Easter and movable feast dates for any yearAsh Wednesday, Palm Sunday, Easter, Ascension, Pentecost — they all move together. Get the full table for Western and Orthodox calendars.Give a photo a two-color duotone lookSpotify-cover style: map a photo's tones onto a shadow-to-highlight gradient of two brand colours.Make a photo look like newsprintThe halftone dot screen: an image rebuilt from variable-size dots, like a newspaper photo seen up close.Resize a folder of images in one passTwenty product photos need the same max width for the web shop. Batch-resize them and download one ZIP.Print a big PDF poster on regular paperA one-page A0 drawing won't fit the home printer. Tile it across A4 sheets with overlap, tape it together.Make a PDF grayscale before printingColour pages on a mono printer can come out muddy or expensive. Convert to grey first — and know what you lose.Delete blank pages from a scanned PDFThe double-sided scan picked up every blank back — half the file is empty pages. Find and drop them by ink coverage.Join audio clips into one fileTwo voice memos become one podcast segment; song parts become a single track. Order them, join, download a WAV.Pull still frames from a videoThe exact frame with the error message; a contact sheet of a clip. Extract evenly-spaced frames or every N seconds as JPEGs in a ZIP.Play Snake in the browserThe Nokia classic: eat, grow, don't hit the wall. Keyboard or touch, three speeds, best score kept locally.Study with flash cards you made yourselfPaste the vocabulary list you're studying as front|back lines, and run the deck — flip, mark, repeat — without accounts or upload.Format messy CSS into readable rulesInherited minified one-liner? Paste it in, get it back with real indentation — or minify clean CSS the other way.Lay out a page with CSS gridColumns, rows, gaps, spans — tune a grid in a live preview and copy the CSS for parent and items.Turn JSON records into SQL INSERT statementsAn array of objects from an API or export becomes ready-to-run INSERTs — pick the table name and dialect, copy, run.Make two identical-looking strings compare equalMac filenames and pasted text sometimes fail matching even though they look identical — Unicode normalization is usually the fix.See what a floating-point number really holdsWhy is 0.1 + 0.2 not 0.3? Inspect the sign, exponent, and mantissa bits any number actually stores.Look up an ASCII codeDecimal, hex, octal, binary, and the character — for one code point or a browsable table of all 128.Reverse a string, word order, or line orderPalindrome checks, flipped word order, last-line-first output — three reversal modes for a pasted block.Pull the numbers out of a reportFigures buried in paragraphs — paste the text, get every number with its context, plus a total and count.Read and write military timeFlight boards and schedules say 1830 or 18:30 — convert between 24-hour, 12-hour, and compact forms.Convert a date to a Julian day numberAstronomy tables and data pipelines use JD and MJD instead of calendar dates — convert both directions.Work out the score you need on the final examTarget grade, current average, and the final's weight — the weighted-average math answers 'what do I need on the final?' in one line.Size a voltage divider for a sensor or level shiftDrop 5 V to 3.3 V for an ADC, or check an existing resistor pair — enter any three values, get the fourth and the nearest standard resistors.Convert between betting odds formatsA book shows +150, an article says 5/2, a site displays 3.50 — one number, three dialects, plus the implied probability.Fit a trend line to your dataPaste x,y pairs from a spreadsheet and get the least-squares slope, intercept, R², and predictions — no chart software needed.Find a compound's molar massType a formula like Ca(OH)2 or CuSO4·5H2O and get the molar mass plus the element-by-element breakdown.Estimate gravel for a bed, path, or drivewayArea and depth in, tonnes and bags out — metric-first with imperial equivalents, material densities, and a waste margin.Lock the answers into a filled PDF formYou filled in a PDF form — now flatten it so the values can't be edited, before emailing or archiving it.Rebuild duplex pages from two one-sided scansYour feeder scans one side only — fronts in one PDF, backs in another (often reversed). Interleave them back into one document.Change a GIF's playback speedA screen-recording GIF crawls, or a meme plays too fast — scale every frame's delay or set a fixed one.Bring a quiet recording up to a usable levelA voice memo peaks at −20 dB and everyone cranks their volume — normalize to a target peak and export a WAV.Play tic-tac-toe against an unbeatable computerMinimax plays perfectly — the best you can do is draw. Or pick casual mode, or pass the device to a friend.Hide a note inside an imageLeast-significant-bit steganography: tuck a text message into a PNG's pixels, invisibly — and extract it back.Make an app icon set from one square imageOne 1024×1024 master becomes every iOS and Android size in a ZIP — opaque for iOS, transparency kept for Android.Order enough wallpaper for a roomMeasure the walls once, then translate perimeter, height, roll size, and pattern repeat into a roll count you can order with.Figure board feet before buying lumberBoard feet is how hardwood is priced. Convert thickness, width, length, and count into the volume unit the lumberyard charges by.Read a roof pitch in any notationRise-over-run, degrees, percent grade, and x/12 all describe the same slope. Convert between them and get the angle and common-rafter factor.Make a dilution that hits a target concentrationC₁V₁ = C₂V₂ solves any single unknown — how much stock to take, how much solvent to add, or what concentration you end up with.Count and round significant figuresWhich digits carry precision and which are padding? Count significant figures in any written number and round to a chosen count.Read a slope from two pointsRise over run, angle, percent grade, and the line equation from any two points — or from slope plus one point.Do a logarithm calculation by hand checkCommon, natural, and arbitrary-base logarithms plus antilogs — the pocket check for decibels, pH, and exponential growth work.Add, subtract, and project vectors2D and 3D vector arithmetic — sum, difference, dot product, magnitude, angle, and the projection of one vector onto another.Depreciate an asset and read the scheduleStraight-line and declining-balance depreciation from cost, salvage, and life — the annual schedule and remaining book value.Find your break-even pointFixed costs, price per unit, and variable cost per unit produce the unit count and revenue where profit turns positive — plus a margin of safety.Read a z-score back into plain languageHow many standard deviations from the mean is a value — and what share of the distribution sits above or below it? Percentile, one- and two-tailed areas.Read a confidence interval for a meanFrom a sample mean, spread, size, and confidence level to the interval — z or t critical value, margin of error, and what the range means.Read a three-digit capacitor codeCeramic and film capacitors print a 3-digit code plus a letter — decode it to picofarads and tolerance, and go the other way too.Fix up a messy .env fileLint a dotenv file — flag duplicate keys, bad quoting, and invalid lines, with every value masked in the report.Write an .editorconfig without the guessworkPick indent style, size, line endings, and charset; get a valid .editorconfig file with the common sections filled in.Write .htaccess rules without memorizing syntaxHTTPS redirect, www canonicalization, custom error pages, and caching headers — compose them into a valid Apache .htaccess file.Make an SVG wave dividerLayered smooth waves as copy-pasteable SVG — tune amplitude, frequency, layers, and colors for section dividers and hero backgrounds.Make an SVG blob shapeOrganic rounded shapes for avatars, backgrounds, and masks — seeded, smooth SVG paths you can copy or download.Name a color from its hex codeWhat is #f2a154 called? Match any hex color against the CSS named-color table and see the nearest names with distances.Make an Open Graph image in the browserThe 1200×630 image that shows when a link is shared — title, subtitle, accent color, and footer on a clean canvas, exported as PNG.See an audio file's waveform without a DAWDrop a WAV, MP3, or OGG and get a waveform plot plus peak/RMS levels and duration — a quick loudness and clipping check.Get quick statistics from a CSV columnPaste or drop a CSV and get per-column counts, min/max, mean, median, and standard deviation — enough to sanity-check data before the real analysis.Play memory (concentration) soloFlip two cards, find the pairs. Three difficulties and a move counter — a clean solo concentration game.Solve the fifteen puzzle with hintsSlide the tiles into order on a 4×4 board — scramble, count moves, and get a hint when stuck.Convert degrees to radians (and back)Angles show up in degrees, radians, gradians, and turns depending on the field — here is how to move between them and read DMS.Check if an A/B test is significantTwo conversion rates, one question: is B actually better, or is it noise? The two-proportion z-test gives a yes/no at p < 0.05.Multiply and invert small matrices2×2 and 3×3 matrices cover most homework and graphics math — add, multiply, invert, or take the determinant without a CAS.Pick a survey sample sizeHow many people to ask before the answer means anything: Cochran's formula turns confidence and margin into a headcount.Plan monthly savings toward a goalHow long until the goal at this deposit — and how much of the total is interest? A month-by-month simulation gives both.Work out print dimensions from pixelsA 3000×2400 photo at 300 DPI prints at exactly 10×8 inches — the px↔DPI↔size math, both directions.Convert recipe oven temperatures180°C, 350°F, gas mark 4 — the same moderate oven. Convert between Celsius, Fahrenheit, gas marks, and fan settings.Total up timecard hoursClock in, clock out, subtract the break — per day and for the whole period. Overnight shifts handled.Convert AWG to mm and resistanceAWG 22 is 0.644 mm — wire gauge to diameter, cross-section, and copper resistance per length, in both directions.See one date in other calendarsWhat is today in the Hebrew, Islamic, or Persian calendar? One Gregorian date, eight renderings, plus the ISO week number.Tune CSS easing curvescubic-bezier(0.25, 0.1, 0.25, 1) is CSS's default ease — see the curve, feel a preview, and copy the value.Write a Content-Security-Policy headerdefault-src 'self'; script-src 'self' cdn.example.com — assemble a CSP from checkboxes instead of remembering the syntax.Embed a file as a data URIdata:image/svg+xml;base64,… lets you inline assets in CSS or HTML without a second request — generate one locally.Set up a CSS flexbox layoutRow or column, wrap or not, space-between or center — set the container properties, watch the preview, copy the CSS.Test glob patterns before using themDoes src/**/*.ts match src/app/page.tsx? Test *, **, ?, [class], and {a,b} against a path list before committing it to config.Query JSON with JSONPath$.store.book[*].title pulls every title — test JSONPath expressions against real JSON and see exactly what matches.Look up a port numberWhat listens on 5432? What port does Redis use? A searchable table of the well-known TCP/UDP assignments.Tidy messy SQLOne-line SQL pasted from a log becomes readable: keywords uppercased, clauses on their own lines, consistent indent.Fade audio in and outHard starts and abrupt cuts sound amateur — a linear or equal-power fade at each end fixes it in one pass.Play audio backwardsReverse a recording sample-for-sample — hear hidden phrasing, check a mix tail, or just hear what backwards sounds like.Change audio speedDouble-speed lecture, half-speed practice track — tape-style resampling moves pitch with tempo, exactly like a tape deck.Tune an instrument by ear and meterA microphone tuner that shows the nearest note and how many cents sharp or flat you are — no app, no account.Crop a passport or ID photoA passport photo is a portrait at exact dimensions — pick the document size, frame the crop, export at print resolution.Pack a sprite sheetFifty small images, one HTTP request — pack them into a PNG atlas with a JSON map of where each frame landed.Repeat text for testing and templatesNeed "item, " 200 times, or a numbered list skeleton? Repeat any string with a separator and optional numbering.Measure how different two texts are"Almost the same" is a number — Levenshtein distance counts the edits between two strings, and the percentage makes it readable.Play Connect FourDrop a disc, block the computer, connect four. The classic 7×6 gravity game against a beatable AI or a friend.Solve Lights OutEvery press flips a cell and its neighbors — get all five-by-five lights off. Solvable by construction, with a hint when stuck.Decode what a tire size like 205/55R16 actually meansThe string on the sidewall encodes width, profile, and rim. Here is how to read it — and how much a different size would change your speedometer.Estimate blood alcohol after drinksA Widmark estimate for 'how much is still in me' — and the honest caveat that no calculator can tell you it is safe to drive.Work out a half-life — or what remains after itRadioactive decay, medication clearance, capacitor discharge — the same equation solves for whichever of the four numbers you do not have.Find a material's density from mass and volumeWeigh it, measure it, divide. The calculator also runs backwards — how much does 2 L of mercury weigh?Solve any speed–distance–time questionTrip planning, homework, 'how long is a marathon at 12 km/h' — one equation, three solvable fields, four speed units.Convert cups to grams for a recipeA cup of flour and a cup of honey do not weigh the same. Per-ingredient conversion keeps American recipes usable on a scale.Work out the dew point — and what it feels likeCondensation on windows, sticky summer air, fog risk — all read off one number computed from temperature and humidity.Read the wind chill before going out−5 °C in a gale is not −5 °C. The NWS formula turns temperature and wind into the number your skin actually feels.Read the heat index on a humid dayHumidity stops sweat from cooling you. The heat index is the 'feels like' temperature once that brake fails.Work out profit on a stock tradeBought at one price, sold at another, commissions on both sides — the net number, the %, and the break-even sell price.Estimate body fat with a tape measureNo scale, no calipers — the US Navy circumference method turns three or four tape measurements into a body-fat estimate.Split a calorie target into protein, carbs, and fat2,000 kcal at 40/30/30 is how many grams of each? Gram targets are what labels and food scales actually measure.Plan a staircase from floor-to-floor heightTotal rise in, riser count and total run out — plus the stringer length and angle for cutting lumber.Work out what overtime adds to a paycheckHours past the threshold pay a multiplier — plug in rate, hours, and the multiplier and see the effective hourly rate too.Compare the four 'ideal weight' formulasDevine, Robinson, Miller, Hamwi — they disagree by kilograms because each was fit to a different insurance table. Seeing all four keeps any single one honest.Convert steps to distance — 10,000 steps is how far?Fitness trackers count steps; distance is what matters for routes and calorie math. Stride length is the missing piece.Work out the exact gap between two ages'Born March '88 and June '91' is not instantly a number. Birthdates in, calendar-exact difference out.Set an alarm when your phone is not handyA browser-tab alarm for a time like 07:30 — with an honest warning about what a page timer can and cannot do.Find which fiscal quarter a date lands inNot every fiscal year starts in January — pick the start month and get the quarter dates, or check where a date sits inside one.Clip a page element into a shape with CSSHexagon avatars, angled section edges, diamond photos — clip-path does it without image editing. Build the shape, copy the CSS.Turn a CSV export into an HTML tablePaste spreadsheet CSV, get a clean escaped <table> you can drop into a page — no script, no server.Write a manifest.json that browsers acceptPWA install prompts, taskbar icons, splash colors — all driven by one JSON file that fails silently when a field is malformed.Target every nth element with CSSStripe table rows, clear floats on every third card, style the last item — nth-child patterns with a live 24-item preview.Stack text shadows for depth and glowOne shadow reads flat; two or three stacked layers make glows, outlines, and retro depth. Build up to four layers with live preview.Read what a User-Agent string is claimingEvery browser sends one; most are now deliberately bland. Parse the tokens to see claimed browser, engine, OS, and device class.Make a uniform photo grid without an editor2–12 photos, same-size cells, even gaps — the layout math and center-crop are done for you, out comes one PNG.Change an image's DPI tag for printingThe print shop asked for 300 DPI — the fix is a metadata tag, not a resize. Read and rewrite DPI on JPEG/PNG without touching pixels.Mix two audio files into oneVoice memo over a backing track, or two takes summed together — per-track gain and optional peak limiting, out as WAV.Make a batch of QR codes from a listSixty equipment tags, a sheet of table numbers, URLs for a flyer run — one QR per line, all bundled into one ZIP.Summarize a long text without sending it anywhereExtractive summarization keeps the sentences that carry the text's own vocabulary — private, instant, and honest about what it is.Measure an investment's annual growthTurn a start and end value into the one smoothed rate that connects them — CAGR.See every payment of a loanA monthly payment is one number; the schedule shows where each payment actually goes.Convertir el consumo entre paísesUna reseña de EE. UU. usa mpg, un catálogo japonés km/L, una ficha europea L/100km — la misma eficiencia en tres dialectos.Convert a tire or gauge pressureThe pump reads bar, the door sticker says psi, the manual is in kPa — translate between them.Convert engine power and kilowattsSpec sheets split between hp, PS, and kW — and the two 'horsepowers' don't even match.Work out a gear ratioTeeth in, ratio out — plus what the output shaft actually spins at.Mix two-stroke fuel50:1 on a 5-liter can is not a guess — get the exact oil volume.Pick the drill before the tapThe hole before the thread: the tap drill size for metric and imperial taps.pH from a concentration, and backAny one of pH, pOH, [H⁺], [OH⁻] unlocks the other three — the 25 °C relations in one step.ABV from gravity readingsTwo hydrometer readings bracket the fermentation — OG before, FG after, ABV between them.Pick a video bitrate for a target sizeFit a recording into a file size or a length — solve whichever of bitrate, size, duration is missing.Plan a RAID array's capacityFive drives do not mean five drives of storage — RAID levels trade capacity for survivability.How far to sit from the TVScreen size and shape set the sweet spot between immersion and eye strain — the field-of-view way.How much house can this income affordLenders screen by debt-to-income; run the 28/36 rule yourself before they do.Reformat one date every way at onceA date needs ISO for the database, RFC for the email header, and a custom pattern for the report — write it once.Validate or convert JSONLOne JSON object per line is great until line 4,317 is broken — find every bad line at once.Read a Cookie or Set-Cookie headerCookie headers are dense one-liners; a table turns attributes into something checkable.Check the share card before postingThe link preview is your landing page's first impression — see what the OG tags produce before sharing.Test a version against a semver rangeWill 1.4.2 satisfy ^1.2.0? Ask before the package manager answers for you.Preview pasted HTML in a sandboxIs this markup safe to embed? Render it in an isolated frame instead of your page.Audit a site's security headersEight headers carry most of a page's browser-side defense — check which are present and sane.Compute bitwise operationsAND a mask, set a flag bit, shift a register value — see the binary while you do it.Personalize one template into many messagesDear {{name}}, your order {{id}} ships {{date}} — plus a CSV of rows gives every message at once.Pull every email address out of textMinutes, logs, a web page's source — the addresses hiding inside come out one per line.Apply many replacements in one passTwenty find-replace pairs applied at once beats twenty trips through a one-pair dialog.Draw Secret Santa pairsNobody draws themselves, couples can be excluded — a fair assignment in one shuffle.Darken a photo's edgesA vignette pulls the eye to the center — a smooth radial darkening you control.Read an image's histogramThe exposure truth-teller: are the shadows crushed, the highlights gone, the channels balanced?Make a texture tile seamlesslyEdges that wrap into each other — a texture that repeats without a visible grid.Posterize a photoN levels per channel turns a photo into flat bands — the graphic look of screen-print and propaganda posters.See a sound as an imageA spectrogram makes pitch visible — voices, bird calls, and hums drawn as frequency over time.Fix subtitle cues directlyA typo in cue 14, a start time that trails the audio — edit the lines instead of reconverting.Read a video file's metadataHow long, how big, how sharp — the basics of a clip without opening an editor or uploading anything.Get the images out of a PDFThe photo embedded in a report is trapped at full quality — pull the original image data, not a screenshot.Pon a prueba tu memoria numéricaEl clásico de Human Benchmark: los dígitos aparecen, desaparecen y los escribes — un dígito más cada ronda.Test your sequence memoryNine tiles flash in a pattern; replay it. The pattern grows one step every level.Try the chimp testYoung chimps beat college students at this: numbers appear on a grid, hide after your first click, and you finish the order from memory.Controlar la cafeína del díaDos cafés y un té — ¿cuánto es eso, y cuándo se elimina lo bastante para dormir?Planear cuánto de la foto queda nítida¿Retrato a f/1.8 o paisaje a f/11? Dónde aguanta el enfoque de verdad y dónde está la hiperfocal.Estimate your FIRE numberThe 25× rule says you need 25 times annual spending — this shows the target and how many years to reach it.Plan a debt payoff orderPay the highest rate first (avalanche) or the smallest balance first (snowball) — see months and interest for both.Convert torque specs to horsepowerAn engine quote gives lb-ft at RPM — the same curve in horsepower is one multiplication away.Work with decibelsTwo 80 dB machines are not 160 dB — decibel math is logarithmic, and this keeps it honest.Check if the spool has enough filamentSlicers quote meters; spools are sold by weight. Convert between them before a long print.Size an off-grid solar setupCabin, van, or shed — daily watt-hours turn into panel watts and battery capacity.Measure pool water and dose chlorineChemical doses are per gallon — get the pool's volume right first, then the ppm you need to add.Estimate the fertile windowCycle tracking puts ovulation ~14 days before the next period — the fertile window around it is what planning needs.Scale a bread formulaBaker's percentages make a recipe scale to any flour weight — 65 % water stays 65 % at 500 g or 5 kg.Check voltage drop on a cable runLong 12 V runs lose volts to wire resistance — size the cable before the load browns out.Time a capacitor's chargeAn RC pair charges toward the rail on an exponential curve — τ tells you how fast.List every upcoming paydayBiweekly checks don't come on the same date — lay the next year of paydays out in a row.Find your age on other planetsA Mercury year is 88 days — you're centuries old there, and barely a toddler on Neptune.Express an IP range as CIDR blocksAllow-lists take CIDR notation — a start–end range splits into the minimal covering blocks.Inspect a HAR captureA HAR file is the browser's request log — who was called, how long it took, and how much moved.Write JSON-LD structured dataRich results need schema.org markup — generate Article, FAQ, Event, or Product JSON-LD from a form.Search and replace with a real regexEditor find/replace can't capture groups — swap (\d+)px to $1 pixels, flag by flag, in one pass.Try bold-fixation readingBionic-style text bolds the start of each word — some readers find it keeps the eye moving.Count what a message costs in SMS partsOne emoji can double your bill — GSM-7 fits 160, Unicode fits 70, and concatenation trims both.Mask sensitive text before sharingLogs and pastes carry emails, cards, and IPs — redact the patterns before the snippet leaves your hands.Turn a photo into a cross-stitch chartPixel grids are stitch grids — a photo downsampled to cells and a small palette is a workable pattern.Make a deterministic name avatarSame name, same avatar — initials or a symmetric identicon, no account needed.Swap one color in an imageBrand color changed? Swap #ff0000 to #00aa44 across a whole image without repainting.Cut the silent edges off audioRecordings start and end with dead air — trim to the first and last sound automatically.Pull vocals out of a stereo trackLead vocals usually sit dead-center — subtract the middle and the backing track stays.Measure how loud audio really isStreaming platforms normalize to LUFS — measure integrated, momentary, and short-term loudness plus peak.Fill a PDF form without printingApplication forms arrive as PDFs — type into the actual fields instead of printing, writing, and scanning.Play a 5-letter word guessSix tries, three colors, one word — the wordle-style loop in a browser, no app needed.Practice mental math for a minuteSixty seconds, rising difficulty, integer answers — a warm-up for interviews or a brain break.Test yourself with the Stroop effectRED printed in green — say the ink, not the word. A classic attention test in twenty rounds.Place a projector for the screen size you wantA 120-inch screen does not fit wherever the projector happens to sit. Work out the lens-to-screen distance before you drill the mount.Match exposure when you change aperture or ISOMetered f/2.8 at 1/125 s and ISO 100, but you need f/8 for depth of field. How many stops, and which shutter keeps the same exposure?Plan a timelapse: how many frames, which intervalA 30-second sunset clip at 30 fps takes 900 frames. To squeeze two hours into it, the camera must fire every 8 seconds.Compare bike gears before you buy or shiftIs 52/11 meaningfully harder than 50/12? Gear inches and development turn cassette choices into numbers you can compare.Predict your race time from a recent resultYou ran 10K in 45:00. What does that say about a half marathon? The Riegel formula turns one result into equivalent times.Size a rainwater collection setupHow many liters does a roof actually deliver? Area times rainfall times a runoff coefficient — then check it against daily use.Estimate a shipment's CBM and chargeable weightFreight charges on whichever is worse: real weight or volume weight. Compute CBM, volumetric kg, and what you'll actually be billed for.Check an investment with NPV and IRRSpend 100k now, get 30/40/50/40k back over four years. At a 10% hurdle rate that is +25k of value — and the IRR says by how much it clears.Find where an LC circuit resonatesAn inductor's reactance rises with frequency, a capacitor's falls. Where they cross is the resonant frequency — compute it before you wind a coil.Design a 555 blinker without the datasheet algebraTwo resistors and a capacitor set the blink rate. Try R and C for a target frequency, or read the duty cycle you already have.Cut an antenna to length for your frequency145 MHz needs a 49 cm quarter-wave whip. The same formulas scale from HF wire dipoles to a 2 m full-wave loop.Gauge a horizontal tank from a dipstickA half-full drum is not at half height. Circular-segment math converts dipstick depth into litres — or the depth for a target fill.Test an XPath against real XMLBefore the scraper ships, check that //item[price>100] really selects what you think — on your own document.Decodificar un secreto base32Las claves TOTP y los tokens seguros para DNS llegan en A–Z2–7. La decodificación base32 muestra los bytes; la codificación verifica el viaje de ida y vuelta.Leer el código fuente de un correo quoted-printableEl código fuente de un correo muestra Caf=C3=A9 au lait. La decodificación quoted-printable devuelve los escapes =XX al café que enviaste.Embed an image in firmware as a C arrayMicrocontroller displays take pixels as byte arrays, not PNG files. Convert a splash image into a header you can #include.Write an SPF record for your domainv=spf1 is easy to get subtly wrong — one extra include can blow the 10-lookup limit. Assemble the record from checkboxes instead of memory.Write a DMARC record that reports before it rejectsStart at p=none, read the reports, then tighten. The builder assembles p/sp/rua/pct tags without you memorizing the syntax.Make an email signature that survives Gmail and OutlookRich signatures break in transit. A single table with inline styles is the markup mail clients reliably keep — build one plus a plain-text fallback.Write braille patterns without a braille keyboardUnicode braille patterns (⠓⠑⠇⠇⠕) let you typeset braille in documents. Convert English text to grade-1 patterns and back.Binarize a scan for clean printingGrey washout, shadows at the spine, uneven lighting — thresholding turns a photo of a page into true black on white.Inspect an image's channelsA noisy JPEG often hides the noise in one channel. Split R, G, B, and alpha into grayscale views to find it.Flatten a transparent logo for print or office suitesA transparent PNG turns into a black smear in some print pipelines and a gray checkerboard in slides. Composite it onto a chosen color once.Extract one channel from a stereo recordingInterview recorded with the mic on the left only? Pull that channel to mono — or isolate mid/side for analysis.Generate DTMF keypad tonesTest an IVR, feed a modem, or demonstrate touch-tone encoding — the two-tone beeps for any digit string, as a WAV.Make a binaural beat toneLeft ear 200 Hz, right ear 204 Hz — a listener hears a 4 Hz beat. Generate the stereo WAV instead of trusting a streaming app.Count your Schengen days90 days in any rolling 180 — entry and exit days both count. List your stays and see how much room is left, or when a new stay must end.Find the sun's angle at a place and timeWill the sun clear the neighbor's roof at 3 pm in December? Elevation and azimuth for any coordinates and UTC time.Run a random draw with a spinning wheelLunch order, raffle prize, who goes first — list the entries and spin. Uniform odds, one winner per spin.Practice visual scanning with a Schulte tableFind 1 to 25 in order on a shuffled 5×5 grid, timed. A classic drill for widening your useful field of view.Time your cube solvesScramble, solve, stop — then watch best, mean, Ao5, and Ao12 update. Practice-grade scrambles and WCA-style averages.Strip comments and markup from a PDF before sharingReview comments, highlights, and link annotations travel with the file. Strip every annotation before the PDF leaves your hands.Measure a room's floor area before buying flooringFlooring is sold by the square metre — here is how to measure an L-shaped room and add the right waste margin.Transpose a chord sheet to fit your voiceThe song is in C but your singer needs E♭. Shift every chord at once without retyping the sheet.Convert dBm readings to watts and voltsA spectrum analyzer says −13 dBm — is that safe for the next stage? Convert it to mW and Vrms before you connect anything.Estimate how many drywall sheets a room needsWalls minus doors and windows, plus waste — a sheet count you can take to the store.Plot a function to sanity-check homework or dataType the expression and see the curve — quicker than a graphing calculator when you just need the shape.Solve PV = nRT for the missing variableThree knowns, one unknown — pressure, volume, moles or temperature, with unit conversion built in.Solve a constant-acceleration problem with three knownsEnter any three of u, v, a, t, s and get the other two — the suvat equations applied for you.Work out the shutter speed under an ND filterND1000 turns a 1/250 s exposure into 4 seconds. Compute the new shutter before you're standing in the field.Estimate how far a projectile travelsLaunch speed and angle in — range, flight time and peak height out. The classic physics problem, minus the algebra.Convert a centrifuge's RPM to ×g (RCF)Protocols specify 10,000 ×g, but the centrifuge dial says RPM. The rotor radius links them — convert properly.Evaluate expressions a basic calculator can'tTrig, logs, powers and factorials in one typed expression — with a history to pull old results from.Add an integrity hash to a third-party script tagCDN scripts can change underneath you. An SRI hash makes the browser refuse a tampered file — here is how to generate one.Generate IDs that sort by creation timeUUIDs are random; ULIDs encode time so sorting the string sorts the chronology — useful for log and record keys.Test your 2FA setup with a local TOTP generatorYou're building OTP verification and the QR enrolment works — but does your backend accept the codes? Generate RFC 6238 codes locally to check.Turn a JSON payload into XML for a legacy APIThe integration wants XML but your data is JSON. Convert the structure — elements, arrays, escaping — without hand-writing tags.Move an INI config into JSON for a modern toolLegacy app config lives in an INI file; the new service wants JSON. Convert sections to nested objects without retyping.Inspect a TOML config as JSON to debug itIs that dotted key landing where you think it is? Converting pyproject.toml or Cargo.toml to JSON makes the resolved structure obvious.Reflow a pasted document to 80 columns (or back)Mailing-list replies and README prose want hard-wrapped text; copied PDFs arrive hard-wrapped and need joining. Both directions, one paste.Strip accents from names for ASCII-only systemsJosé → Jose, Zoë → Zoe, Łukasz → Lukasz — when the form, airline or database only accepts A–Z.Decode a Vigenère cipher for a puzzle huntARGs and geocache logs still love the classic cipher. Encrypt or decrypt with a keyword — learning-grade, not security.Give photos a retro dithered lookFloyd–Steinberg grain or Bayer's ordered grid — the print-and-dot aesthetic of 90s screens, on any photo.Sharpen a soft photo without making it crunchySlight blur from a missed focus or a resized image: unsharp masking puts the edge back — if you don't overdo it.Spot clipped highlights and shadows in a photoThe histogram says the photo is clipping — but where? False colour paints the lost zones so you can decide if they matter.Test speakers and rooms with a frequency sweepA slow sweep from bass to treble exposes rattles, resonances and dead spots that single tones hide.Check an MP3's tags before you share itThat ripped file may carry a comment with your name, or a cover you didn't choose. Read what's inside before it goes anywhere.Score a bowling game without doing the arithmeticSpare bonuses, strike chains and the three-ball tenth — tap the pins and let the scoring rules work.Explore Conway's Game of Life on a drawable boardThree rules, endless complexity. Draw cells, drop gliders and still lifes, and watch emergent behaviour unfold.See how six sorting algorithms actually differBubble's slow crawl, quicksort's partitioning, merge's divide-and-conquer — replayed as bars so the idea lands visually.Check whether a sudoku puzzle is solvable and uniqueStuck on a puzzle — or building one? The solver returns the solution and counts whether it's the only one.Black out parts of a PDF so they stay goneDrawing a rectangle over text in an editor doesn't remove it — the content stays underneath, selectable. Rasterized redaction actually deletes it.Read a certificate or CSR without installing opensslA PEM block or .crt file you can't open locally — drop it in and read the subject, issuer, validity window and SANs directly.Turn a JSON response into Go structsHand-writing struct fields for a 40-field API payload is how typos ship. Paste the sample, get the structs with tags.Turn a JSON response into Python dataclassesTyped API code without hand-writing every field. Paste the response, get @dataclass classes with Optional where the sample needed it.Convert pasted HTML into JSX you can drop into Reactclass becomes className, for becomes htmlFor, style strings become objects — the mechanical part of porting markup, done at once.Turn a JavaScript object literal into valid JSONConsole output, fixtures and config snippets quote keys only sometimes and use single quotes. Strict JSON parsers reject all of it — this rewrites it properly.Verify a downloaded file with its checksumThe download page says CRC-32 is 3f8a2c1e. Instead of trusting it, compute the checksum yourself and compare.Decode Base58 text without grabbing the wrong alphabetBase58 exists because 0/O/I/l look alike — but three different alphabets use that name. This codec uses the Bitcoin one.Add a LICENSE file with the correct text'MIT licensed' isn't a file — GitHub and package registries look for the actual text. Generate it with your name and year already filled in.Publish a security.txt that researchers can actually useSomeone found a hole in your site — where do they report it? RFC 9116 defines the answer, and this writes the file for you.Read the timestamp hiding inside a Discord snowflakeEvery Discord ID is a timestamp plus bookkeeping. Decode the 19-digit number to find when a message, user or server was created.Mint MongoDB ObjectIds for fixtures and test dataSeed data needs IDs that sort by creation and look real. Generate a batch of proper 24-hex ObjectIds without a database.Check an SSH key fingerprint before you trust it'Are you sure you want to continue connecting?' is only a question if you can verify the answer. Paste the public key, get the fingerprint to compare.Convert an XML plist to JSON (and back) without a MacInfo.plist files, .mobileconfig profiles, Apple config dumps — XML plists parse to editable JSON here. Binary plists are rejected; convert with `plutil -convert xml1` first.Convert an oven recipe for the air fryer (or back)The recipe says 200°C for 30 minutes — your air fryer needs lower and shorter. The rule of thumb, applied both directions.Size a position before you enter the trade'How much can I buy?' is the wrong question — it's 'how much can I lose?'. Risk a fixed percent and let the stop set the size.Scale pizza dough by hydration, not by vibesBaker's percentages turn 'a bit wetter than last time' into exact gram weights — flour first, everything as a percentage of it.Project dividend income over the next decadeA yield today isn't the yield on your cost later. Model growth and reinvestment and see when the checks get interesting.Dial in coffee and water by brew ratioRecipes say 1:16 like it's obvious. It means 1 gram of coffee per 16 grams of water — here's the number either direction.Extend an arithmetic, geometric or Fibonacci sequenceHomework sequences and pattern puzzles: pick the rule, get the next hundred terms — or ten thousand — with the Nth term on demand.Find the p95 in a pile of latency numbersThe average says 40ms but users are complaining. The percentile view shows the tail the mean hides.Estimate how long an EV charge actually takesA 150kW charger never delivers 150kW the whole session. Model the taper past 80% and the loss at the wall.Find the frequencies your room exaggeratesBass that booms in one corner and vanishes in another isn't your speakers — it's standing waves. Your room's dimensions tell you where they sit.Estimate boards for a deck before you buyDeck area ÷ board coverage undersells the gaps and the cuts. Count rows, then boards per row, then waste.Order enough soil for raised beds without guessing'How much soil?' is a volume question with a bag-count answer — length × width × depth, then divide by the bag size.Make a passphrase you can actually typeX7!q2#k is strong and untypeable. 'orbit walnut shelf radio' is strong and types itself — random words beat random symbols for humans.Pluralize English words without the classic bugs'1 item' / '3 items' is easy until the word is 'memory' or 'criterion'. Rule-based pluralization that knows its exceptions.Check whether a phrase is a palindrome — punctuation ignored'A man, a plan, a canal: Panama' is a palindrome once you strip what's not letters. Check phrases, or find the off-by-one that's ruining yours.Fix text typed in the wrong keyboard layoutруддщ was 'hello' typed with the Russian layout on; likewise umlaut swaps on QWERTZ/AZERTY. Remap it back character by character.Add a clean border around a photo for print or postPrints need breathing room; feeds crop edge-to-edge. A uniform border in any colour, added without touching the photo.Turn a heightmap into a normal map for a game engineGrayscale bumps don't light properly — engines want the purple normal map. Convert height to surface direction per pixel.Pixelate a photo into sprite-ready artReference photos become sprite bases by quantization: downscale hard, limit the palette, upscale crisp — no smoothing.Pull the audio track out of a video fileThe meeting recording has the audio you need; the screen recording has the sound effect. Decode the video, keep the sound, get a WAV.Check how high you can still hearHearing rolls off at the top with age — 17kHz at 20, 14kHz at 40 is typical. A staircase test finds your ceiling.Call bingo numbers for a group without a cage1–75, shuffled and called one at a time, with the letter columns announced — the caller part of a bingo game, minus the plastic balls.Practice code-breaking logic on MastermindSix colours, four positions, twelve guesses — every guess returns black and white pegs. The classic deduction puzzle, solvable every time.Solve nonograms with logic, not guessingRow clues like '3 1' mean a run of 3, a gap, a run of 1. Cross the rows against the columns and the picture fills itself.Invert a PDF's colours for night readingWhite pages on a dark screen glare. Flip every page to dark-mode — the PDF becomes white-on-black rasterized pages.Write an ads.txt file that ad systems can actually readOne malformed line can make a whole ads.txt unreadable to crawlers. The format is four comma-separated fields — here is how to assemble it without the usual mistakes.Convert coordinates to geohash (and back) without surprisesA geohash is a cell, not a point — decoding gives an area, never the exact original coordinate. Precision, cell sizes and what decode actually returns, in one place.