About the ISBN Validator & Converter
Every book's ISBN carries a check digit. Enter an ISBN-10 or ISBN-13 with or without hyphens to confirm it's valid and convert it to the other format. Handy for booksellers, librarians, authors setting up listings and developers cleaning product catalogues.
How to use it
- Enter an ISBN-10 or ISBN-13.
- See whether the check digit is valid.
- Copy the converted format.
Tips and good to know
- ISBN-10 check digits can be X, meaning 10.
- ISBN-13s starting 978 convert to ISBN-10; 979 ones don't.
- Hyphen positions vary by publisher, so they're ignored here.
- Barcodes on books (EAN-13) encode the ISBN-13.
About developer tools
Developer utilities are some of the most-searched tools online because everyone who touches code needs them, and they are usually needed right now: a minified API response to read, a Base64 string to decode, a token to inspect, a regular expression to debug. The risk with many online versions is that you paste secrets — API keys, tokens, customer data — into a server you know nothing about.
Every developer tool here runs entirely in JavaScript inside your browser tab and uses the standard Web Crypto and encoding APIs where relevant. You can open your browser's network panel and confirm that nothing is transmitted when you use them. Even so, treat production secrets with care: rotate any credential you have shared anywhere you did not intend.
These utilities follow the relevant open standards — RFC 8259 for JSON, RFC 4648 for Base64, RFC 3986 for URL encoding, RFC 7519 for JSON Web Tokens and FIPS 180-4 for the SHA family of hashes — so results match what your servers, libraries and command-line tools produce. Where browsers differ from other runtimes, such as JavaScript's regular expression flavour, the page says so. They are deliberately small and dependency-free so they load quickly on slow connections and keep working as browsers evolve. If a result surprises you, the guide on each page lists the most common causes, which are usually invisible characters, encoding mismatches or copied whitespace.
Popular ways people use developer tools
- Reading a minified API response while debugging an integration or a webhook payload.
- Inspecting a login token to see which claims it carries and exactly when it expires.
- Building and testing a regular expression for form validation before shipping it to users.
- Generating unique IDs for test fixtures, seed data or database migrations.
- Producing a checksum to confirm that a downloaded or copied file has not been altered.
How we build and test our free tools
Every tool in this collection is built and tested by The Curator team. Before a tool is published we check it against known reference results — textbook loan schedules, standard test vectors for hashes, sample files for conversions — and we re-check it whenever browsers change. Each page explains the method so you can verify the answer yourself rather than take it on trust.
The tools run as JavaScript inside your browser tab. When you choose a file, your browser reads it from your disk into memory; the tool processes it and gives you the result as a download. No copy is sent to us or to anyone else, and nothing is kept after you close the tab. That is why these tools are safe for personal documents, and why they keep working on a slow or interrupted connection once the page has loaded.
The collection is free because it is supported by advertising on these guide pages. We never charge for a tool, never add watermarks and never sell what you type. If something doesn't work as described, or you would like a tool we don't have yet, please contact us — new tools are added in regular batches based on what readers ask for.
Frequently asked questions
- Does a valid ISBN mean the book exists?
- No — only that the number is well-formed.
- Why did my ISBN-10 change its last digit when converted?
- ISBN-13 uses a different check-digit formula, so the last digit is recalculated.
- Is my input stored or sent anywhere?
- No. Everything runs inside your browser tab and disappears when you close it.
- Is the ISBN Validator & Converter really free?
- Yes. There is no account, no trial and no watermark. The Curator is supported by advertising on its guide pages, never by charging for tools or selling your data.
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