Developer
Regex Tester
Test and debug regular expressions with live matching and explanations.
Why regex is still both loved and hated
Regular expressions are powerful for pattern matching, but they are easy to get subtly wrong, especially with greedy quantifiers, Unicode, and line-ending differences. A tester helps you see matches against sample strings, which is faster than guessing with deploy cycles.
Use the tool
A disciplined workflow
Start with small samples that include your edge cases, then add complexity. If you are using flags like multiline or dot-all, re-read what they do in your engine. If a pattern will process untrusted input, also think about performance traps like catastrophic backtracking; a tester can show a match but not a denial-of-service risk under load.
Dialect differences
JavaScript, PCRE, and other engines have differences. The behavior on this page matches the environment the tool is built in—treat the result as a development aid, not a proof for every platform.