Regex Tester
Write a pattern, paste some text, and see every match highlighted along with its capture groups. Presets for the patterns everyone reaches for — email, URL, IP, dates — are one click away.
Runs entirely in your browser. Nothing you paste is uploaded.
About the Regex Tester
Patterns run through the browser's native JavaScript regex engine, so behaviour here matches what your frontend code will do exactly. Note that JavaScript's flavour differs from PCRE, Python's re, and Go's RE2 in meaningful ways: no atomic groups, no possessive quantifiers, and lookbehind support that varies by engine age.
The flags that matter: g finds every match rather than just the first, i ignores case, m makes ^ and $ match at line boundaries, and s lets . match newlines.
Frequently asked questions
Which regex flavour is this?
JavaScript's, running natively in your browser. Most basic syntax is portable, but avoid atomic groups and possessive quantifiers if the pattern also needs to work in PCRE or RE2.
Why did my browser freeze on a pattern?
Catastrophic backtracking. Nested quantifiers like (a+)+ can take exponential time on non-matching input. Rewrite the pattern to avoid ambiguity about where each repetition ends.
How do I match across multiple lines?
Use the s flag to let . match newlines, and the m flag to make ^ and $ match at each line boundary rather than only at the start and end of the whole string.