---
title: "ISBN Validator - Free Online ISBN Check | CanDoYa"
description: "Free online ISBN validator for ISBN-10 and ISBN-13. Check digits, normalize hyphens, handle X and see clear invalid reasons."
url: https://candoya.com/tools/isbn-validator/
locale: en
type: browser-tool
---

# Free ISBN Validator

Category: Developer

## What does an ISBN validator do?

An ISBN validator checks whether a book identifier is structurally valid. Paste an ISBN-10 or ISBN-13 and this tool removes spaces and hyphens, verifies the correct check digit, flags unsupported prefixes, and shows the normalized value. It runs locally in your browser.

The validator uses the official ISBN check-digit rules: **ISBN-10 uses modulo 11 with X as 10**, while ISBN-13 uses the EAN-13 alternating 1 and 3 weight pattern. It also checks that ISBN-13 values start with the Bookland prefix 978 or 979.

## How to use it

1. **Paste the ISBN** - Enter an ISBN-10 or ISBN-13 with or without hyphens and spaces.
2. **Read the status** - The result updates live and explains whether the identifier is valid or why it fails.
3. **Check the digit** - Compare the expected check digit with the digit found in the input when a typo is detected.
4. **Copy the normalized value** - Copy the compact ISBN, or use the equivalent ISBN-10 or ISBN-13 conversion when one exists.

## Who it's for

- **Editors and publishers** checking book metadata before sending it to stores, printers or catalog systems.
- **Developers** validating ISBN fields in imports, forms, CSV cleanup jobs or test fixtures.
- **Librarians and booksellers** confirming whether a typed identifier is an ISBN-10, ISBN-13 or a likely typo.
- **Students and researchers** normalizing citation data without uploading a bibliography.

## Expert note

A valid check digit proves the number is well formed, not that a specific title exists or that the publisher block is currently assigned. Treat validation as an error check for typed identifiers, then confirm bibliographic metadata against your catalog source.

## Frequently asked questions

### Is the ISBN validator free?

Yes. The ISBN validator is free to use with no sign-up, no download and no usage limit. Paste an ISBN, read the validation details and copy the normalized number when you need it.

### Is my ISBN uploaded anywhere?

No. The check runs in your browser using client-side JavaScript. That keeps book lists, inventory exports, manuscripts and citation drafts on your device while you validate the identifier format.

### Does it support ISBN-10 and ISBN-13?

Yes. It validates ISBN-10 numbers with a digit or X check digit and ISBN-13 numbers with a 978 or 979 prefix. For valid 978 ISBN-13 values, it also shows the equivalent ISBN-10.

### Why can ISBN-10 end with X?

ISBN-10 uses a modulo-11 check digit, so the calculated value can be 10. The standard writes that value as X, and it is only valid as the final character, never in the middle of the ISBN.

### Why does an ISBN-13 need to start with 978 or 979?

ISBN-13 is part of the EAN barcode system for books. The 978 and 979 Bookland prefixes identify book numbers; a 13-digit code with another prefix may be a valid EAN, but it is not an ISBN.

### Can this prove a book really exists?

No. It verifies the structure and check digit only. A valid ISBN can still be unassigned, reused incorrectly or attached to metadata that needs checking in a publisher, library or bookseller database.

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*Markdown edition of <https://candoya.com/tools/isbn-validator/>, published for AI agents and other automated readers. Index of key pages: <https://candoya.com/llms.txt>.*