Regex without the deploy-and-pray loop
Regular expressions are powerful, terse, and notoriously easy to get wrong. A single misplaced quantifier can match the entire string instead of just the bit you wanted; a forgotten flag can make a case-sensitive expression silently miss results. Iterating on a regex against a deployed environment is slow; iterating in a live tester is fast.
This tester uses the JavaScript RegExp engine built into your browser. Every match is highlighted as you type, with capture groups, indexes, and the full match list visible at all times. A replace preview shows you exactly what the resulting string will be — no surprises in production.
Supported flags
- g — global, return every match instead of just the first.
- i — case-insensitive.
- m — multiline, ^ and $ match at line boundaries.
- s — dotall, . matches newline characters too.
- u — unicode, full Unicode escapes and properties.
- y — sticky, anchor at lastIndex.
- d — has indices, expose start and end of each capture.
Common gotchas
Greedy versus lazy quantifiers (.* versus .*?), the difference between a character class and a group, the way alternation binds with grouping, and the subtle behaviour of zero-width assertions all trip up experienced developers. Use the live highlighter to confirm that your pattern matches what you think it matches before pasting it into a code review.