Developer & Web Tools
Regex Tester
Test regular expressions against sample text with live match highlighting and capture groups.
Privacy
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Tips
- Without the g flag only the first match is returned. That is the single most common reason a pattern "does not work".
- The m flag makes ^ and $ match at line boundaries rather than only at the start and end of the whole string.
- This uses the JavaScript regex engine. PCRE, Python and Go differ in places — lookbehind support and named-group syntax in particular.
- Nested quantifiers such as (a+)+ can trigger catastrophic backtracking on non-matching input. If a pattern hangs elsewhere, that is usually why.
- In replace mode, $& is the whole match, $1 is the first group, and $<name> is a named group.
Frequently asked questions
Why does my pattern behave differently in my code?
Check the flags and the escaping. A pattern written in a string literal needs its backslashes doubled — \\d in JavaScript source is \d in the pattern. Entering it here directly avoids that layer.