Regex Tester
Build, test and debug regular expressions live in your browser — instant match highlighting, capture groups, substitution preview, a plain-English explanation and ready-to-paste code for 15+ languages.
Runs entirely in your browser using the native JavaScript regex engine — nothing is uploaded. The generated code lets you take the same pattern to 15+ languages.
The global (g) flag is recommended to replace every match.
Live testing uses the JavaScript engine. Some flavors (Go, Rust) do not support look-arounds or back-references.
About Regex Tester
The Regex Tester lets you build, test and debug regular expressions live: type a pattern, paste a test string, and matches are highlighted instantly with every capture group — numbered or named — listed with its exact index range. It runs entirely in your browser on the native JavaScript regex engine; nothing is uploaded.
Beyond matching, four extra tabs do the heavy lifting. Substitution previews a replacement with $1, $2 and $<name> group references. Explanation breaks the pattern down token by token in plain English. Code generates ready-to-paste snippets for 15+ languages, and Reference keeps character classes, anchors, quantifiers and look-arounds one click away.
Common patterns — email, URL, IPv4, IPv6, UUID, dates, slugs, hex colors and more — load as one-click presets, and all six flags (g, i, m, s, u, y) toggle from checkboxes. Invalid patterns are flagged immediately instead of failing silently, making this a practical regex tester online for daily work.
How to use Regex Tester
- Type your regular expression, or load one of the presets (email, URL, IPv4, UUID…).
- Toggle the flags you need — g for all matches, i for case-insensitive, m for multiline.
- Paste a test string and inspect the highlighted matches and capture groups.
- Use the Substitution tab to preview replacements, or Explanation for a token-by-token breakdown.
- Open the Code tab and copy the pattern as a working snippet in your language.