Check whether an ISBN is typed correctly
A 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.
Tools used in this guide
The job
ISBNs end with a check digit that catches the two most common typing mistakes: a wrong digit and a transposed pair. Validating before a bulk import prevents silent failures where an API lookup returns nothing.
How to do it
Paste the ISBN with or without hyphens — spaces are ignored too. The tool reports valid/invalid, which format it parsed, and the correct check digit when the entered one is wrong. Valid 978-prefixed ISBN-13s also show the ISBN-10 equivalent.
- ISBN-10 uses a weighted sum mod 11, and the check digit can be X (meaning 10).
- ISBN-13 uses alternating 1/3 weights mod 10, same as a barcode's check digit.
Worked example
Cataloging a paperback you type 4060000001 and the tool flags it invalid — the expected check digit is 0, not 1, which suggests a slip in the middle digits rather than the last one. Fixing the typo produces 4060000000-adjacent valid numbers only when the whole sequence matches.
Limits
Check-digit validity is necessary but not sufficient — a syntactically valid ISBN may not be assigned to any book, so pair this with a catalog lookup for real verification. Conversion to ISBN-10 exists only for 978-prefixed ISBN-13s; 979-prefixes have no ISBN-10 form. Registration-group hyphens are not inserted — output is the bare digits.