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.