Isbn Validate Validator🔒 100% local
Validate ISBN-10 and ISBN-13. Privacy-first, no server uploads, no tracking.
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Checks an ISBN-10 or ISBN-13 by recomputing its check digit from the other digits, ignoring hyphens and spaces as it goes, and shows the weighted sum it used along the way. An ISBN-10 also gets its 978-prefixed ISBN-13 equivalent, with a freshly computed check digit. The sums are plain arithmetic in the page, so no catalogue, retailer or library API is queried and nothing you type is associated with what you are looking at.
How to use it
- Paste an ISBN, with or without hyphens; the box starts with 9780134685991.
- Press Process.
- Read the Verdict line and the checksum, and use the suggested digit when a transcription went wrong.
Worked example
9780134685991becomesInput: 9780134685991
Digits: 13 (ISBN-13)
Verdict: ✓ VALID ISBN-13
GS1 prefix: 978 — Bookland (classic)
Check digit: given 1, computed 1 (match)
Checksum: weighted sum 129 mod 10 ✓
Formatted: 978-0-1346-8599-1Check: 9x1 + 7x3 + 8x1 + 0x3 + 1x1 + 3x3 + 4x1 + 6x3 + 8x1 + 5x3 + 9x1 + 9x3 = 129, so the digit is (10 - 129 mod 10) mod 10 = 1, which is the digit already there.
9780134685990becomesInput: 9780134685990
Digits: 13 (ISBN-13)
Verdict: ✗ INVALID — check digit mismatch
GS1 prefix: 978 — Bookland (classic)
Check digit: given 0, computed 1 (MISMATCH)
Checksum: weighted sum 129 mod 10
Try recomputing: expected last digit 1.One digit changed breaks the sum. The tool prints the digit that would make it pass, which is how you spot a transposition.
043942089XbecomesInput: 043942089X
Digits: 10 (ISBN-10)
Verdict: ✓ VALID ISBN-10
Checksum: weighted sum 209 ≡ 0 (mod 11) ✓
ISBN-13 equivalent would be: 9780439420891The X counts as 10: 10x0 + 9x4 + 8x3 + ... + 1x10 = 209, divisible by 11. Prefixing 978 and recomputing gives the 13-digit form.
When to use it
- Checking a hand-typed ISBN from a book's copyright page before it goes into a catalogue.
- Working out which digit is wrong when a scanner read fails and the title is obvious.
- Converting an old ISBN-10 record to the 13-digit form a system now demands.
What it does not do
- It validates the number, not the book: an unused but well-formed ISBN still comes back VALID, and nothing is checked against any registry.
- It expects exactly 10 or 13 digits once hyphens and spaces are stripped. Anything else returns the length message, and a stray letter throws an error unless it is the trailing X of an ISBN-10.
- The ISBN-10 conversion assumes the 978 prefix and cannot tell you anything about 979, which is not derivable from an ISBN-10.
- The grouping in the Formatted line is fixed at 3-1-4-4-1, so it is a display convention rather than the registration group the publisher actually uses.
- Duplicate detection, publisher ranges and whether a registration group exists are all out of scope.