Test regular expressions with real-time match highlighting. Debug and validate regex patterns. Free online developer tool. This tool runs entirely in your browser — no data is sent to any server. It's fast, free, and works on any device.
Testing regular expressions interactively is the fastest way to build and debug them. Instead of running your code, checking output, adjusting, and repeating — this tool highlights matches in real time as you type. You can see exactly what your pattern captures, which groups match, and where it fails. The tool supports all JavaScript regex features including named groups, lookaheads, lookbehinds, and Unicode properties. Common use cases include building data extraction patterns, testing input validation rules, crafting search-and-replace operations, and learning regex by experimenting. The real-time feedback loop makes the difference between spending 5 minutes or 50 minutes on a complex pattern.
This uses JavaScript's built-in RegExp engine, which follows the ECMAScript standard. It supports most modern features including lookbehinds (ES2018), named groups, and Unicode property escapes.
Common issues: forgetting the 'g' flag for multiple matches, unescaped special characters (use \. for literal dots), incorrect character class ranges, or the pattern is too specific. Try simplifying and building up.
Enable the 'm' flag to make ^ and $ match line starts/ends instead of string start/end. Also consider the 's' flag which makes '.' match newlines (dotAll mode).
Most patterns transfer directly. Minor differences exist — JavaScript uses /pattern/flags syntax while Python uses re.compile('pattern', flags). Named groups differ: JavaScript (?
Groups are portions of the match captured by parentheses. In '(\d{3})-(\d{4})', matching '555-1234' gives Group 1: '555', Group 2: '1234'. Named groups show their names. Use groups for extracting specific parts of matches.