ISBN Validator
Validate a 10- or 13-digit ISBN by verifying its check digit, and detect which format it is. Runs entirely in your browser — nothing is uploaded.
Batch check (one ISBN per line)
Validate an ISBN
Paste a 10- or 13-digit ISBN (hyphens and spaces are fine) to verify its check digit, see its bundled registration group and normalized digits, and get the ISBN-10↔13 equivalent when available. Batch-check many at once or generate a valid example — all locally in your browser.
FAQ
What is the difference between ISBN-10 and ISBN-13?
ISBN-10 is the older 10-digit format; ISBN-13 is the current 13-digit book format using 978 and assigned 979 registration groups. Both have a check digit, and the tool converts between them when an equivalent exists.
Why is my ISBN invalid?
The tool explains the reason — wrong length, wrong prefix, or a bad check digit (it even shows the digit that was expected).
How is it validated?
ISBN-10 uses a weighted sum modulo 11 (the last digit can be X for 10); ISBN-13 uses alternating 1/3 weights modulo 10.
Why doesn't it show a fully hyphenated ISBN?
Registrant (publisher) ranges vary in length and can only be split correctly with the International ISBN Agency's current Range Message. This tool shows the bundled registration group and normalized digits instead of inventing publisher and title segments.
Can I check many at once?
Yes. Open Batch check and paste one ISBN per line; each is validated with its type and the reason for any failure.
Does it check the book exists?
No. It only validates the format and check digit — not whether a real book is registered to it.
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