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ISBN Validator / Converter

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Validate an ISBN-10 or ISBN-13 checksum and convert a valid ISBN to the other format where possible

Paste an ISBN-10 or ISBN-13 and get its check digit verified against the format's own checksum algorithm, with the format inferred automatically from the character count once hyphens and spaces are stripped. ISBN-10 uses a mod-11 checksum that can produce an 'X' check digit, while ISBN-13 shares the same weighted mod-10 algorithm as EAN-13 barcodes. A valid ISBN-10 is also converted to its ISBN-13 equivalent by prefixing 978 and recomputing the check digit, and a valid ISBN-13 converts back to ISBN-10 only when it actually starts with that 978 prefix, since ISBNs issued under the newer 979 prefix have no ISBN-10 equivalent. It doesn't look up what book an ISBN actually belongs to, since that would require a paid publishing database and this tool only validates the checksum and converts the format.

isbnbookchecksumvalidatorpublishing

How to use ISBN Validator / Converter

  • 1.Paste an ISBN-10 or ISBN-13, with or without hyphens, to see whether its check digit is valid.
  • 2.Check the converted field to get the equivalent ISBN-13 (from an ISBN-10) or ISBN-10 (from a 978-prefixed ISBN-13).
  • 3.Use it to sanity-check ISBN data before importing it into a catalog, or to generate the companion format for an existing ISBN.

Frequently asked questions

How is ISBN-10 vs ISBN-13 determined?
It's inferred purely from the character count after hyphens and spaces are stripped: 10 characters is ISBN-10, 13 is ISBN-13.
Why does an ISBN-10 sometimes end in the letter X?
The ISBN-10 checksum is a mod-11 algorithm, which can produce a check value of 10; by convention that's written as the letter X rather than two digits.
Why doesn't every ISBN-13 convert back to an ISBN-10?
ISBN-10 to ISBN-13 conversion works by prefixing 978, so only ISBN-13s that actually start with 978 have a valid ISBN-10 equivalent. Newer books issued under the 979 prefix (once the 978 range is exhausted in a given range) have no ISBN-10 form at all.
Does this look up the actual book the ISBN belongs to?
No, it only validates the checksum and converts the format; looking up a real book would require a paid publishing database, which is out of scope for this tool.

Use via API, SDK, or MCP

cURL# Free: 1,000 req/day · Pro: 10,000 req/day
curl -X POST https://api.utilix.tech/v1/tools/isbn-validator \
  -H "Authorization: Bearer utx_live_..." \
  -H "Content-Type: application/json" \
  -d '{"isbn":"0-306-40615-2"}'

Get an API key from your dashboard · Full API docs →

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