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.

Tools used in this guide

The job

ROT13 is the internet's classic spoiler-hiding convention, and Caesar shifts turn up in CTF challenges and puzzle hunts. Decoding means shifting each letter back — trivial once you know the shift, annoying by hand.

How to do it

Paste the text. For ROT13 use Caesar with shift 13; for anything unknown, pick “try all 25 shifts” and scan the list for readable words. Atbash (A↔Z mirror) and ROT47 (which also scrambles digits and symbols) are one click each.

ROT13 applied twice returns the original — it is its own inverse.
Only ASCII letters move; Japanese text, numbers, and punctuation pass through Caesar untouched. Use ROT47 for ciphertext containing digits.

Worked example

“Uryyb, jbeyq!” looks like noise until shift 13 reveals “Hello, world!”. In “try all shifts” mode the output table lists all 25 decodings, and the readable line is usually obvious at a glance.

Limits

This is a toy cipher — anyone can decode it instantly, so never use it to protect real information (the site's text-encryption tool exists for that). Non-ASCII characters are untouched, and “try all shifts” decodes only the first 200 characters of the input.