ISBN Validator
Check ISBN-10 and ISBN-13 numbers in bulk: valid or invalid, the correct check digit, the ISBN-13 form, registration group and likely typo.
Every ISBN ends in a check digit calculated from the other digits, so most typing mistakes, such as one wrong digit or two neighbouring digits swapped, make the number invalid. Paste one ISBN or a whole list, one per line, to see which are valid, what the check digit should be, the matching ISBN-13 and the registration group (the language area or country agency).
How to use this tool
- Paste one ISBN, or several on separate lines. Hyphens, spaces and an "ISBN" prefix are ignored.
- Read Valid or Invalid and the correct check digit.
- For an invalid number, look at the suggested transposition, the most common typing error.
- Copy the ISBN-13 for catalogues, shop listings and barcodes.
Formula
ISBN-10: 10·d1 + 9·d2 + 8·d3 + … + 2·d9 + 1·d10 ≡ 0 (mod 11)
ISBN-13: d1 + 3·d2 + d3 + 3·d4 + … + 3·d12 + d13 ≡ 0 (mod 10)
In an ISBN-10 the check value 10 is written as X, and only in the last position. An ISBN-13 must start with 978 or 979, the EAN prefixes reserved for books. Converting an ISBN-10 to ISBN-13 means putting 978 in front and recalculating the check digit.
Example
For 0-306-40615-2: 0×10 + 3×9 + 0×8 + 6×7 + 4×6 + 0×5 + 6×4 + 1×3 + 5×2 = 130, and 130 + 2 = 132 = 12 × 11, so it is valid. Its ISBN-13 is 978-0-306-40615-7. If that ISBN-13 is typed with a final 8, the tool reports Invalid and says the check digit should be 7.
Frequently asked questions
Does a valid ISBN mean the book exists?
No. Valid only means the digits are consistent with each other. Whether a publisher really assigned the number is recorded by the national ISBN agency and book databases, which this offline checker does not query.
Why is no transposition suggested?
Only swaps of two neighbouring digits are tried. A single wrong digit, or two separate mistakes, cannot be fixed by a swap. An ISBN-13 also cannot detect a swap of neighbouring digits that differ by 5, such as 1 and 6, so that mistake still looks valid. ISBN-10 catches every such swap.
What is the registration group?
The digits after 978 or 979 identify a language area or country agency: 0 and 1 for English, 2 French, 3 German, 4 Japan, 7 China, 89 and 979-11 Korea, 979-8 the United States. This tool knows the one- to three-digit groups; the full ISBN International range list also says where the hyphens go.
Sources
Last updated: 2026-10-30