JavaScript Regex Tester
Test RegExp patterns against sample text with highlighting and timeout protection.
When to use this tool
- Testing a regex against a representative block of sample text.
- Debugging why a capture group is not firing in production.
- Teaching regex basics — live highlighting of matches and groups.
How it works
- Paste the sample text.
- Enter the pattern and flags.
- Read the highlighted matches and capture group table.
- Iterate until the right matches are highlighted and no false positives appear.
Privacy: This tool runs entirely in your browser. Your input is not sent to our servers.
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Frequently asked questions
Does it protect against catastrophic backtracking?
There is a timeout guard. If your regex hangs, the tester aborts and warns you before the tab freezes.
Which regex engine is used?
JavaScript's native `RegExp`, which matches the engine in Node.js, Cloudflare Workers, and the browser.
Can I test PCRE-specific features?
No. For PCRE or .NET regex features, use a language-specific tester. This tool targets the ECMAScript regex subset.