ISBN Validator

How to use it

1. Paste an ISBN into the field: 10 or 13 characters, with or without hyphens or spaces.
2. Click Validate to see whether the check digit matches and how the number breaks down.
3. Use Convert to ISBN-13 or Convert to ISBN-10 to move between formats; the result lands in the copy field.
4. Read the structure table: prefix element, registration group, publisher prefix, publication element, provided check digit and expected check digit.
5. Clear the field and start over, or load the Sample to see a worked ISBN-13.

Common use cases

• Catching typos in a catalogue - a transposed digit changes the weighted sum, so a bad ISBN is reported instead of silently accepted.
• Preparing data for a library system - many import templates require ISBN-13; convert the older ISBN-10 values before submitting.
• Reading where a book was published - the registration group tells you the language or country area the publisher belongs to.
• Checking a supplier feed - run a batch through the tool before loading it into your own database.
• Teaching how the check digit works - the expected check digit is shown next to the one you typed.

Why it stays private

Every calculation runs in your browser's memory. The ISBN you type is never uploaded, so unpublished title lists, supplier catalogues and internal identifiers stay on your device.

FAQ

Q: What is the difference between ISBN-10 and ISBN-13? A: ISBN-10 uses a modulus 11 check digit that can be the letter X. ISBN-13 prepends the 978 or 979 bookland prefix and uses a modulus 10 check digit with alternating 1 and 3 weights. Any ISBN-10 can become an ISBN-13, but only 978-prefixed ISBN-13 values have an ISBN-10 form.

Q: Why is the publisher prefix sometimes missing? A: Splitting the publisher prefix from the publication element needs the publisher range table for that registration group, and several of those ranges change over time. The tool splits them only where its built-in table has the ranges and shows the combined segment otherwise, rather than guessing a boundary.

Q: Does an ISBN that passes the check digit exist as a real book? A: Not necessarily. The check digit only proves the number is well formed. A structurally valid ISBN can belong to a cancelled or unassigned title, so confirm the record against your supplier or a national library catalogue.

Q: My registration group shows as unlisted. Is the ISBN invalid? A: No. It means the number falls outside the registration group ranges this tool carries. The check digit verdict is computed independently of that table and remains accurate.