// free tool
Regex Tester
Test JavaScript regular expressions with live matches, flags, capture groups, named groups, and replacement output. Everything runs locally in your browser.
A regex tester validates a regular expression pattern against sample text and shows each match, index, capture group, and replacement result. This tool uses the browser's JavaScript RegExp engine and keeps your text private because matching happens client-side.
pattern
//
Flags
matches
3 foundapi-204 completed in 84ms
auth-401 failed after token refresh
billing-200 completed in 129ms
profile skipped because no match
Capture groups
match 1 · index 0
api-204
groups: $1=api · $2=204
match 2 · index 26
auth-401
groups: $1=auth · $2=401
match 3 · index 62
billing-200
groups: $1=billing · $2=200
Replacement output
api status=204 completed in 84ms auth status=401 failed after token refresh billing status=200 completed in 129ms profile skipped because no match
// faq
Frequently asked questions
- Is this regex tester private?
- Yes. The regular expression and sample text are evaluated entirely in your browser. Nothing is uploaded, logged, or sent to a server.
- Which regex engine does this use?
- This tester uses the JavaScript RegExp engine available in modern browsers. It supports flags such as g, i, m, s, u, named capture groups, lookaheads, and lookbehinds in browsers that support them.
- Can I test capture groups and replacements?
- Yes. The tool lists each match, index, full match value, numbered capture groups, named groups when present, and a live replacement preview using JavaScript replacement syntax like $1 or $<name>.
- Why does a regex work here but not in another language?
- Regex syntax varies by engine. JavaScript, Python, PCRE, .NET, and Java each differ slightly in lookbehind, Unicode classes, named groups, and replacement syntax. Use this tool for browser and Node.js-compatible patterns.
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