Regex Tester
Experiment with regular expressions against sample text while keeping runaway patterns from locking the whole interface. Evaluation runs in a Web Worker that can be terminated after a short timeout.
Live preview
0 matches
Hello world. Hello tools.
What this generator does
- Pattern and flags editor.
- Match highlighting and capture-group list.
- Replace preview.
- Execution timeout and input-length guard.
How to use
- Enter a JavaScript-compatible pattern without slash delimiters.
- Choose flags such as g, i, m, s or u.
- Paste sample text.
- Review matches and groups.
- Try replacement text if needed.
Best practices
- Regex behavior is engine-specific; this tool targets JavaScript RegExp.
- Keep production patterns readable and test edge cases.
- A timeout means the pattern may be too expensive for the sample.
Frequently asked questions
Why did my pattern time out?
Some patterns create excessive backtracking. The worker is terminated to keep the page responsive.
Does the tester support PCRE-only syntax?
No. It uses the browser’s JavaScript regular-expression engine.
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