Regex Tester
Test regular expressions against text with real-time highlighting. Perfect for developers learning and debugging regex patterns.
About the Regex Tester
Test JavaScript regular expressions against text with editable flags. Global mode lists whole matches; capturing groups are not counted as separate matches. Work runs in a separate browser worker and is stopped after two seconds so difficult patterns cannot freeze the page. Output is limited to 1,000 matches, 10,000 characters per match and 100,000 total match characters; a limit notice means the full result is not shown. Changing input cancels previous work.
Features
- JavaScript pattern and flag controls
- Whole-match results
- Syntax error feedback
- Isolated execution with timeout
- Bounded match output
How to use this tool
The Regex Tester works right in your browser — no signup, no installation. Follow these steps:
- Enter your regex pattern in the pattern field.
- Type or paste your test text in the text area.
- Toggle flags (g, i, m) as needed.
- Matches are highlighted in the text area. Match count is shown below.
Frequently asked questions
Why did my regex time out?
Some patterns require excessive backtracking. The tool stops work after two seconds. Simplify nested repetition or shorten the test text, then try again.
Are all matches displayed?
Results stop at 1,000 matches or 100,000 output characters. Individual matches are clipped at 10,000 characters. The output limit notice identifies partial results.
Using the results
Developers and power users need tools that are exact and private. The Regex Tester runs its logic locally in your browser, returns results instantly, and never transmits your input — handy when you are working with keys, hashes, or data you would rather not paste into a remote service.