Private browser developer tool
Test JavaScript regex patterns with confidence.
Paste a pattern, try real text, and see every match. Everything runs in this browser tab with clear limits for slow or oversized inputs.
Regex Tester
JavaScript RegExp semantics, with a worker timeout.
Do not include the surrounding /slashes/.
Common flags: g all matches, i ignore case, m multiline.
Ready. Matching happens locally.
Matched values
Run a pattern to see matches.
Capture groups
Groups appear for each match.
Your pattern and test text stay in this tab. A Web Worker is stopped after a short budget; this protects the page but does not make every pattern efficient.
Frequently asked questions
Is my test text uploaded?
No. Matching runs in a short-lived Web Worker in this browser tab. The tool does not upload, save, or send your pattern or test text to a server.
Which regex flavor does this tester use?
This tool uses the JavaScript RegExp engine provided by your browser. It is not a PCRE, Python, Go, or .NET compatibility guarantee.
Why did the tester stop a pattern?
Pattern length, test text, result count, and worker time are bounded so a slow pattern cannot lock up the page. Try a smaller sample or a simpler pattern.
How do I test a JavaScript regular expression?
Enter a pattern and flags, paste the text you want to inspect, and review the highlighted matches and capture groups. Matching runs in this browser tab.
Worked example
Start with the Names example, then add the `i` flag to compare case-insensitive results. Without the `g` flag, JavaScript returns the first match only.
Limits to know
This tool uses your browser's JavaScript RegExp engine, not PCRE, Python, Go, or .NET compatibility. Patterns are limited to 2,000 characters, test text to 200,000 characters, and results to 1,000 matches. Inputs are not uploaded or stored.