Regex Tester
Test a regular expression against text.
DeveloperProcessed locally. Your input never leaves your browser.
About
Tests a regular expression against text entirely in your browser. Matches and capture groups update as you type (debounced). The regex actually runs in a background Web Worker with a 1.5-second timeout, so a pathological pattern gets stopped instead of freezing the page — the catastrophic-backtracking warning shown before running is only a best-effort heuristic hint, not a guarantee, so keep patterns and test text reasonably sized regardless.
Enter a JavaScript regular expression, choose common flags, and test it against sample text. Matches and capture groups update after a short delay while execution stays isolated from the page.
What you can do
- Supports global matching plus i, m, s, and u flags.
- Lists match positions and capture groups.
- Runs patterns in a Web Worker with a 1.5-second timeout.
Common uses
- Debug validation or search patterns.
- Check capture groups before using a regex in code.
- Explore how flags change matching behavior.
Frequently asked questions
Which regex flavor does this use?
It uses the regular-expression engine provided by your browser JavaScript runtime.
Can a regex freeze the page?
Execution runs in a background worker. A pattern that exceeds 1.5 seconds is terminated, though you should still keep patterns and test text reasonably sized.