ISBN Validator (ISBN-10 / ISBN-13)
Everyday
An ISBN (International Standard Book Number) uniquely identifies a book edition. ISBN-10 (used until 2007) has a mod-11 checksum that allows 'X' as digit 10. ISBN-13 (used since 2007, also a GTIN-13 barcode) has a mod-10 checksum like UPC codes. This tool detects the format from length, validates the checksum, and offers automatic conversion: ISBN-10 → ISBN-13 by prepending '978' and recomputing the check; ISBN-13 ↔ ISBN-10 only when the prefix is 978 (979-prefixed ISBNs have no ISBN-10 equivalent).
Enter an ISBN above (10 or 13 digits).
Validation = checksum only. It tells you the digits are well-formed, not that a book with that ISBN actually exists. Use a library catalog for that.
How to use
- Paste an ISBN (hyphens, spaces, lowercase 'x' all fine — they're normalized).
- Read the validity status. ✓ valid means the checksum passes.
- Copy the converted alternate format from the panel below.
Frequently asked questions
- What does the 'X' in ISBN-10 mean?
- ISBN-10 uses mod 11, so the check 'digit' can be 0–10. To keep the format 10 chars, 10 is written as 'X' (roman numeral). ISBN-13 uses mod 10 so the check is always 0–9, no X needed.
- Can every ISBN-13 convert to ISBN-10?
- Only if it starts with 978. ISBNs starting with 979 (introduced in 2013 as 978 ran low) have no valid ISBN-10 — older databases that expect ISBN-10 will simply not match those books.
- Why are there so many hyphenations of the same ISBN?
- The hyphens mark prefix / registration group / publisher / title segments, and the segment lengths vary by country and publisher. Validation ignores them. Any hyphenation of the same digits is the same ISBN.
- Is ISBN the same as the barcode on the back of a book?
- Yes, for modern books — the ISBN-13 IS the EAN/GTIN-13 barcode. The 5-digit add-on you sometimes see beside it encodes the price.
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