Regex Tester Online

Writing a regular expression and guessing whether it matches is slow. This tool lets you test a regex against real input text immediately — showing matches highlighted, match count, and captured groups — so you can iterate quickly without switching context.

How it works

The tester uses JavaScript's native RegExp engine to evaluate your pattern against the test string in your browser. Matches are highlighted inline in the text, and any capturing groups are listed separately. Everything updates as you type.

How to use it

1. Enter your regular expression in the pattern field (without surrounding slashes)
2. Set your flags — g (global, find all matches), i (case-insensitive), m (multiline)
3. Paste or type your test string in the text area
4. Matches highlight in real time — group captures appear in the panel below

A few things worth knowing

• JavaScript regex flavour: The engine is JavaScript's built-in RegExp. Patterns that work in Python's re module or PCRE (used in PHP, Perl) may differ — particularly around lookbehind support, \s character classes, and named groups
• The g flag matters for match() vs exec(): Without g, only the first match is found. Enable it to find all occurrences
• Catastrophic backtracking: Some badly written patterns (like (a+)+) can hang the browser on long inputs. If the tool becomes unresponsive, reload the tab

FAQ

How do I match a literal dot, bracket, or other special character? Escape it with a backslash: \. matches a literal dot, \[ matches a literal opening bracket.

What's the difference between .* and .*?? .* is greedy — it matches as much as possible. .*? is lazy — it matches as little as possible. This makes a big difference when your pattern has something after the wildcard.

Can I use named capture groups? Yes. JavaScript supports named groups with the syntax (?<name>pattern). They'll appear in the groups panel labelled by name.

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