An ISBN-13 is the 13-digit identifier printed on every modern book, and the final digit is a checksum that lets scanners and databases catch typos. This tool builds strings that satisfy that checksum so they look and validate like real ISBNs, while the body is random — perfect for seeding a catalog, exercising a barcode renderer, or demoing library software without touching genuine registered numbers.
How it works
Every ISBN-13 begins with a GS1 prefix (978 or 979), followed by registration-group, registrant, and publication digits, and ends with a single check digit. This generator fixes the prefix, fills the next nine positions with random digits, then computes the check digit using the standard algorithm:
- Number the first 12 digits from position 0.
- Multiply even positions by 1 and odd positions by 3, then add all products.
- The check digit is
(10 - (sum % 10)) % 10.
Appending that check digit yields a structurally valid 13-digit ISBN. Optional hyphen grouping splits it into the familiar 978-1-234-56789-0 shape for readability.
Tips and notes
- A scanner or validator will accept these because the checksum is correct, but a lookup against any real bibliographic database will return nothing.
- Use the unhyphenated form when feeding databases that store ISBNs as plain 13-digit strings.
- Never ship random ISBNs to customers — a value you generated today could be assigned to a real book tomorrow.