ISBN Validator: Check a Candidate or List
Use this tool to check whether an ISBN candidate follows the structural rules for ISBN-10 or ISBN-13. It removes spaces and hyphens, checks the length, and then applies the form-specific character, prefix, and checksum checks when the length identifies a supported form. Processing happens locally in your browser. A valid result confirms the number's structure only; it does not verify a book, title, publisher, catalog record, or other metadata.
How to Validate ISBNs
- Choose Single Candidate or Bulk Candidates.
- In Single Candidate, enter one ISBN with or without spaces or hyphens; validation updates automatically.
- In Bulk Candidates, paste candidates one per line or separated by commas; the list updates automatically.
- Review the status, displayed fields, and applicable reasons for each candidate.
- After bulk validation, use Copy CSV or Download CSV to export the latest results.
Read the Validation Result
For a single candidate, the result shows Normalized candidate, length, Detected form, Allowed characters, Structure valid, Prefix valid (ISBN-13 only), and Checksum.
- After spaces and hyphens are removed, 10 characters are treated as ISBN-10 and 13 characters as ISBN-13.
- ISBN-13 candidates must start with
978or979. - ISBN-10 allows a final
Xas its check character. - ISBN-10 uses a modulus-11 checksum. ISBN-13 uses a modulus-10 checksum.
- An unrecognized length returns a length reason before the later form-specific checks.
If the single input is empty, the result displays Enter an ISBN candidate above.
ISBN-10 Conversion and Bulk Results
When an ISBN-10 passes its structure and checksum checks, the tool automatically displays Converted ISBN-13. There is no separate conversion control. The reverse conversion is not performed.
Bulk results show the normalized ISBN, form, length, status, converted ISBN-13 when available, and reasons. Empty bulk input produces no results. The CSV output also includes Prefix OK and Checksum OK columns, and Download CSV uses the filename isbn-validation-results.csv. Copy CSV and Download CSV remain disabled until automatic list validation has created results.
Checks and Limitations
The validator checks structure only. It does not query book databases, catalogs, publisher registries, or metadata, and it cannot confirm that a title exists or is in print. Input is processed locally in the browser and is not uploaded.
Frequently Asked Questions (FAQs)
Does a 'Valid ISBN' result mean the book exists?
No. This tool checks structure only - length, prefix for ISBN-13, and checksum. It does not confirm that a book with that ISBN exists, is in print, or is registered to any title or publisher, and it performs no metadata lookup, catalog search, or purchase action.
What is the difference between ISBN-10 and ISBN-13?
ISBN-10 has 10 characters and uses a modulus-11 checksum. Its final character may be a digit or X. ISBN-13 has 13 digits, starts with 978 or 979, and uses a modulus-10 checksum.
Can every ISBN-10 be converted to ISBN-13?
Yes, every valid ISBN-10 can be converted by adding the 978 prefix to its first nine digits and recalculating the ISBN-13 check digit. Reverse conversion is only defined for an ISBN-13 with the 978 prefix.
Is it safe to paste real ISBNs into this tool?
All processing happens locally in your browser, and the input is not transmitted. ISBNs are public identifiers printed on books.