RegexLab - free, no upload, runs in your browser
RegexLab is a live regular expression tester: type a pattern and test text and every match is highlighted instantly, with a table of matches, indexes, and capture groups, plus a match count and pattern metrics. All evaluation happens in your browser, so patterns built against production data stay private.
The patterns people test are usually built against real production data - server logs, user records, or payment references. Online regex testers evaluate that text on their own servers, and many log the patterns for their own training. Running the test locally means your data and your pattern both stay on your machine.
RegexLab uses your browser's native RegExp engine, so a pattern that passes here will behave identically in Node.js and modern JavaScript.
The highlight shows you where matches land; the table shows you what they actually captured. Each row lists the match, its start index, and every capture group - the part that catches mistakes like a group that captures more than intended, or a quantifier that swallows the next field.
The metrics row reports the match count and test length at a glance, so a pattern that matches zero or matches-everything is obvious immediately.
The JavaScript engine (ECMAScript regex). That is the same engine used in Node.js and modern browsers, so a pattern that works here works there.
g (global), i (case-insensitive), m (multiline), s (dotall), and more - type them into the Flags field.
Yes. Every match row lists its capture groups, so you can verify exactly what group 1, 2, and beyond captured.
No. Pattern evaluation runs in your browser with the native RegExp engine. Nothing is transmitted.
The tool highlights and tabulates up to 5,000 matches and shows the first 200 in the table, which covers realistic test cases.