Free Online Regex Tester
Write the pattern once instead of guessing: every match is highlighted and each group is listed with its position.
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How to use Regex Tester
- Enter the pattern and the flags.
- Paste the test string.
- Read the highlighted matches and groups.
- Open the explanation for a token-by-token breakdown.
Questions about Regex Tester
Why does my pattern work elsewhere but not here?
JavaScript has no look-behind in older engines and no named-set syntax; the tester reports the engine difference.
Does it protect against catastrophic backtracking?
Patterns that explode are timed out with a clear warning instead of freezing the tab.
About Regex Tester
Test JavaScript regex patterns with live matches with our free online Regex Tester. 100% browser-based, fast, and private—no login or file uploads required.
These text and code tools clean and transform strings: count words, convert case, deduplicate lines, encode or decode Base64 and URLs, escape entities, hash, format JSON and compare two versions.
This tool runs in your browser. The file is not uploaded. Everything runs on the text you paste, so you can safely process snippets of code or logs; nothing is sent anywhere, and clearing the box removes it from memory.