Regex Tester

Regular expressions power search-and-replace, form validation, log parsing and web scraping. A regex that works on three test cases often fails on the fourth because of edge cases: empty strings, Unicode characters or greedy matching.

A live tester shows every match highlighted in your sample text. You see capture groups numbered so you know which part of the pattern matched which substring. This is faster than console.logging RegExp.exec() in a loop.

The global (g) flag finds all matches, not just the first. The case-insensitive (i) flag treats A and a as equal. Multiline (m) changes how ^ and $ behave across lines. Without the right flags, your pattern silently returns fewer matches than expected.

Catastrophic backtracking can freeze browsers on badly designed patterns with nested quantifiers. If your tester hangs, simplify the pattern or use atomic groups. Test against realistic input lengths, not just three-word strings.