Regex Tester
Test regular expressions with live match highlighting, capture groups, and flag toggles — debug your regex instantly. Free, client-side regex tester.
🔒 100% Client-Side Processing
Your data is processed entirely in your browser and never transmitted to any server.
//g
Frequently Asked Questions
- What regex flavor does this tester use?
- JavaScript (ECMAScript) regular expressions — the same engine as Node.js and every browser. Most PCRE syntax carries over, but PCRE-only features like possessive quantifiers, atomic groups, and recursion are not supported. Lookahead, lookbehind, named groups, and Unicode escapes all work.
- What do the g, i, m, and s flags do?
- g (global) finds every match instead of stopping at the first; i makes matching case-insensitive; m makes ^ and $ anchor at each line instead of the whole string; s makes the dot (.) match newline characters too.
- Why does my pattern hang or run slowly on long input?
- Usually catastrophic backtracking — nested quantifiers like (a+)+ or ambiguous alternations force the engine to try exponentially many paths. Rewrite so alternatives cannot match the same text, or anchor the pattern. This tester caps output at 1,000 matches to stay responsive.
- Is my data private when I use this tool?
- Yes. This tool runs entirely in your browser using client-side JavaScript — nothing you type is transmitted to, logged by, or stored on any server. You can safely process confidential text, tokens, or code.