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ISBN validator

Verify the validity of any 10-digit (ISBN-10) or 13-digit (ISBN-13) International Standard Book Number. This tool strips hyphens and spaces, calculates the weighted modulo 11 or modulo 10 check digit, confirms whether the checksum matches, identifies the country or language registration group (such as UK and English-language publishing areas), and converts between ISBN-10 and ISBN-13 formats. Calculations run entirely in your browser with zero data sent to external servers.

Client-Side ValidationValidation and checksum calculations run in this tab. Nothing is logged or uploaded.
Examples:

Hyphens and spaces are optional. Enter any 10 or 13 character book number.

Paste an ISBN-10 or ISBN-13 above or select an example.

Checks the modulo 11 (ISBN-10) or modulo 10 (ISBN-13) checksum and converts between 10 and 13 digit formats.

ISBN validator example

Validating UK Bloomsbury Harry Potter edition

Input: '978-0-7475-3269-9'. Identifies format as ISBN-13, verifies check digit 9, identifies Registration Group 0 (English language / UK area), and provides equivalent ISBN-10 '0-7475-3269-9'.

ISBN validator how-to

  1. Strip all hyphens, spaces, and punctuation from the input. Convert trailing 'x' to uppercase 'X'.
  2. If length is 10: verify 9 digits followed by a digit or 'X'. Compute sum = sum(d_i * (10 - i)) for i=0..8. Check value = (11 - (sum % 11)) % 11. If 10, check digit is 'X'. Compare with actual 10th character.
  3. If length is 13: verify all 13 characters are digits. Compute weighted sum = sum(d_i * (i % 2 === 0 ? 1 : 3)) for i=0..11. Check value = (10 - (sum % 10)) % 10. Compare with actual 13th digit.
  4. For conversion: if valid ISBN-10, prefix 978 and recalculate 13-digit check digit. If valid ISBN-13 starting with 978, strip prefix and recalculate modulo 11 check digit.
  5. Look up registration group prefix (e.g., 0 or 1 for UK/English language area, 2 for French, 3 for German).
  6. Emit formatted hyphenated representation and validation details.

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ISBN validator FAQ

What is an ISBN validator?
An ISBN validator checks whether a 10- or 13-digit International Standard Book Number is well formed by recalculating its check digit (mod 11 for ISBN-10, mod 10 for ISBN-13). This one runs in the browser with nothing uploaded. It does not look titles up in a catalogue.
What is the difference between ISBN-10 and ISBN-13?
ISBN-10 was the 10-digit book standard used until December 2006. In January 2007, the standard transitioned to 13 digits (ISBN-13) aligned with EAN-13 barcodes, typically prefixed with 978 or 979 to expand publishing capacity.
How is the ISBN-10 check digit calculated?
The first 9 digits are multiplied by descending weights from 10 down to 2. The sum modulo 11 is subtracted from 11. If the remainder is 10, the check digit is represented by the Roman numeral 'X'. If 11, it is 0.
How is the ISBN-13 check digit calculated?
The first 12 digits are multiplied by alternating weights of 1 and 3. The sum modulo 10 is subtracted from 10 (or 0 if the remainder is 0), matching the standard GS1/EAN-13 barcode algorithm.
Can all ISBN-13 numbers be converted to ISBN-10?
No. Only ISBN-13 numbers starting with the 978 'Bookland' prefix can be converted back to ISBN-10. ISBN-13 numbers starting with 979 were introduced after the 10-digit system was exhausted and have no ISBN-10 equivalent.
What do the registration group numbers represent?
The registration group identifies the country, territory, or language area. Groups 0 and 1 represent the English-language market (including the UK, United States, Canada, Australia, and New Zealand), group 2 represents French, group 3 German, and group 4 Japan.
Are book numbers checked against a live library database?
No. This tool validates the structural integrity, character set, and mathematical checksum of the ISBN locally in your browser. It does not query commercial catalogue APIs (like Nielsen BookData or British Library) to check title availability.
How can I validate an ISBN programmatically in code?
Strip hyphens and spaces. For 10-digit strings, compute sum(d_i * (10 - i)) % 11 === 0 (treating 'X' as 10). For 13-digit strings, compute sum(d_i * (i % 2 === 0 ? 1 : 3)) % 10 === 0.