ISBN Validator (ISBN-10 & ISBN-13)
Check whether a book's ISBN-10 or ISBN-13 has a correct checksum and instantly see which standard it is — runs 100% in your browser, nothing is uploaded.
Hyphens and spaces are ignored.
🔒 ISBNs are validated in your browser — nothing is uploaded.
Validate any ISBN in seconds
Paste a book number such as 978-0-306-40615-7 and this tool checks its checksum live and tells you whether it is a valid ISBN-10 or ISBN-13. Hyphens and spaces are stripped automatically, so you can copy the number in any common format without cleaning it up first. If the check digit does not match, you get a clear message so you can spot a typo before ordering, cataloguing, or entering the number into a system. For a valid ISBN it also shows the equivalent code in the other standard, converting ISBN-10 to ISBN-13 and back so you can normalise old and new records.
How the checksum works
An ISBN-10 uses a weighted mod-11 checksum: each of the first nine digits is multiplied by weights 10 down to 2, the check digit closes the sum, and the total must be divisible by 11. Because a remainder can equal 10, ISBN-10 allows the letter X as its final check digit. An ISBN-13 instead alternates weights of 1 and 3 across its thirteen digits and must be divisible by 10. This tool applies both rules exactly, so a number only reads as valid when its check digit is genuinely correct.
Frequently asked questions
What is the difference between ISBN-10 and ISBN-13?
ISBN-10 is the older 10-digit format using a mod-11 checksum that can end in the letter X. ISBN-13 is the current 13-digit format (usually starting 978 or 979) with a mod-10 checksum. This tool detects and validates both automatically.
Why is my ISBN showing as invalid?
The most common cause is a mistyped digit, which breaks the checksum. Make sure you have exactly 10 or 13 digits (an X is only allowed as the last digit of an ISBN-10) and that no digits were dropped or transposed when copying.
Is my ISBN uploaded or stored anywhere?
No. Validation runs entirely in your browser with JavaScript — the ISBN never leaves your device, nothing is sent to a server, and the tool keeps working even offline.