Build a custom credit-card regex
Toggle which brands to accept. Optional strip of spaces and dashes. Verify against samples live. Runs locally.
/^(?:4[0-9]{12}(?:[0-9]{3})?|(?:5[1-5][0-9]{14}|2(?:2(?:2[1-9]|[3-9]\d)|[3-6]\d{2}|7(?:[01]\d|20))\d{12})|3[47][0-9]{13})$/How to build a credit-card regex
Toggle which brands to accept; the pattern alternates brand prefixes. Optionally strip spaces and dashes.
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Pick brands
Click any combination — Visa, Mastercard, Amex, Discover, JCB, Diners.
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.
patternECMAScriptliteralliveinput · literalbrands · regexVisa Mastercard Amexloaded · ECMAScriptPCRE · ready - 02
Allow separators
Strip spaces and dashes before matching so '4111 1111 …' passes.
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 · mliveconfig · optionsstrip · flags[x] strip sepsflags applied · liveECMA · live - 03
Verify samples
Drop one PAN per line. Pass/fail surfaces immediately.
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-saferun · outputverify · matchesok 4111111111111111matches · 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.
copyexportclipboardblobexport · exportedready · savedCopiedready to shipsuccess
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.
When to build a card regex
Lock down which card brands your app accepts.
Form input
Limit to brands you actually accept. 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-safeFixture data
Pick valid test PANs by brand. 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-compliantBulk PAN audit
Sanity-check brand distribution. 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-gradeDocumentation
Show what shapes you accept. 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-engineMigrate gateways
Confirm brand coverage matches. 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-readyTeach prefixes
Visualise how prefixes identify brand. 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-readyFrequently asked questions
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Tell us what you need. We ship the top requests every two weeks.