What is the difference between ISBN-10 and ISBN-13?

ISBN-10 (older) is 10 digits with a checksum where the last digit can be X (10). ISBN-13 (current, since 2007) is 13 digits using the EAN-13 checksum, always prefixed with 978 or 979.

How is the check digit calculated?

ISBN-10 uses a weighted sum mod 11 (weights 10 down to 1). ISBN-13 uses an alternating 1-3-1-3 weighting mod 10. The validator runs both checks against the digits before the check position.

Does it confirm the book exists?

No. This is a checksum and format check only. To resolve an ISBN to a title you need an external lookup service.

Yes. Both the regex check and the checksum calculation run in your browser.

isbn-10 · isbn-13 · check digit · batch

Validate ISBN-10 or ISBN-13 with check digit

Regex format check plus the standard mod-11 / mod-10 check-digit verification. Single or batch. Runs locally.

ISBN Validator

Mode

single

one value

Valid

Invalid

fail

Pattern

isbn

ISBN-13

input · single value

samples:

output · result

okValid

Pattern · ISBN-13 /^97[89]-?\d{1,5}-?\d{1,7}-?\d{1,7}-?\d$/

Quick Start

How to validate an ISBN

Switch ISBN-13 (modern) or ISBN-10 (legacy). Format and check digit both must pass.

01
Pick a format
13-digit is the standard since 2007. 10-digit covers older books.
Patterns compile through the JavaScript RegExp constructor, so syntax errors surface immediately and engine quirks like Unicode property escapes (\p{L}) work when the u flag is on.
patternECMAScriptliterallive
input · literalformat · regex
ISBN-13 | ISBN-10
loaded · ECMAScriptPCRE · ready
02
Type or paste
Dashes and spaces are stripped before checking the digits.
Each flag character mirrors the ECMAScript literal: g enables iteration, i folds case, m anchors per line, s lets . match newlines, u unlocks proper Unicode, y is sticky, and d emits indices.
flagsoptionsg · i · mlive
config · optionsvalue · flags
978-3-16-148410-0
flags applied · liveECMA · live
03
Read the verdict
Both regex shape and check digit must pass for a green tick.
Watch for catastrophic backtracking on nested quantifiers — a common ReDoS source. The tool caps match counts to keep the page responsive on pathological patterns.
matchgroupshighlightReDoS-safe
run · outputverify · matches
ok 978-3-16-148410-0
matches · livegroups · live
04
Copy or export
Grab the output as JSON, CSV, or plain text — ready for your editor or pipeline.
Copy writes via navigator.clipboard.writeText; downloads use a Blob and object URL, so nothing transits the network and the output is byte-identical to what you see on screen.
copyexportclipboardblob
export · exportedready · saved
Copied
ready to shipsuccess

Pro tips

Regex patterns that don't melt down

Use named groups

(?<year>\d{4}) reads better than $1 and survives reordering. Supported in ECMAScript 2018+.

Anchor strictly

Use ^/$ with the m flag when matching whole lines. Without anchors, partial matches sneak through.

Avoid catastrophic backtracking

Nested quantifiers like (a+)+ can explode. Run patterns through ReDoS Detector first.

Escape every literal

Backslash any meta character you want literally: \.\$\^\*\+\?\[\]\{\}\|\\.

Test edge cases

Empty string, single character, unicode, the maximum length you expect — write fixtures for each.

Patterns aren’t parsers

Don’t parse HTML, JSON, or balanced parens with regex. Use a proper parser when the grammar is recursive.

Use Cases

When to validate ISBNs

Catalog imports, library cleanup, bookstore feeds.

Catalog import

Sanity-check ISBNs in a publisher CSV. Compiles through the JavaScript RegExp constructor — engine quirks (Unicode property escapes, sticky matching, named groups) work when their flags are on. Error messages cite the exact position of any syntax issue.

ReDoS-safe

Library MARC

Validate ISBNs from a metadata feed. Pairs with the ReDoS detector to catch catastrophic backtracking before you deploy. A pattern that handles 1k-character input fine can become a denial-of-service vector on attacker-controlled 1M-character input.

ECMA-compliant

Bookstore feed

Reject malformed inputs at the edge. Output exports as JavaScript, Python re, Java util.regex, .NET System.Text.RegularExpressions, PCRE, and POSIX — language quirks are highlighted on conversion so you don't ship a JS-only pattern to a Go service.

spec-grade

Migration

Surface bad rows before importing. Capture groups (named or numbered) round-trip cleanly into replacement strings, JSON output, or CSV extraction without re-typing. Backreferences ($1, ${name}) preserve semantics across languages.

cross-engine

Bulk audit

Find the typos in a long list. Test against edge cases — empty input, single character, max length, multibyte boundaries — to catch off-by-one and zero-length match bugs before they reach production.

test-ready

Teach

Show how check digits catch transposition errors. All matching runs client-side so secret patterns never leave the browser. Useful when the pattern itself is sensitive (PII regexes, internal data formats, security filters).

production-ready

FAQ

Frequently asked questions

Difference between ISBN-10 and ISBN-13?

ISBN-13 is the modern 13-digit form. Use ISBN-10 only for legacy books published before 2007.

Is the check digit important?

Yes — without it, almost any 10 or 13 digit string would 'pass'. Check digits catch typos.

What about ISBN-X with 'X' last?

ISBN-10 uses 'X' as a valid check digit (representing 10). Both upper and lowercase x are accepted.

Hyphens required?

No — the validator strips them. Both 'ISBN 978-3-16-148410-0' and the unformatted form are fine.

Is anything sent to a server?

No. The tool runs entirely in your browser — your pattern and sample text never leave the page.

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