ISBN Validator

Reference

What is an ISBN?

An ISBN (International Standard Book Number) is a unique numeric identifier assigned to every published book. ISBN-10 was the original format (10 digits), used until 2007. ISBN-13 is the current standard (13 digits, starting with 978 or 979), aligned with the EAN-13 barcode system. ISBNs are assigned by national ISBN agencies and are essential for cataloging, ordering, and tracking books worldwide.

How ISBN validation works

ISBN-10 uses a weighted checksum: multiply each of the first 9 digits by weights 10, 9, 8, …, 2, add the check digit (where X = 10), and verify the total is divisible by 11.
ISBN-13 uses alternating weights of 1 and 3: multiply each of the first 12 digits by alternating 1 and 3, sum them, and verify that (10 − sum mod 10) mod 10 equals the check digit. Both algorithms catch all single-digit errors and most transposition errors.

ISBN-10 vs ISBN-13

ISBN-10 — 10 characters, check digit is 0-9 or X (representing 10). Can be converted to ISBN-13 by prepending "978" and recalculating the check digit. ISBN-13 — 13 digits, always starts with 978 or 979. ISBN-13 numbers starting with 978 can be converted back to ISBN-10; those starting with 979 cannot. Hyphens or spaces separate the parts: prefix (ISBN-13 only), registration group, registrant, publication, and check digit.

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