Regex Tester
Test regular expressions live: match highlighting, hit count, capture groups for each match, and friendly error messages for broken patterns.
Type a pattern first.
What is it
A regular expression (regex) is a tiny pattern language for finding text. You write a pattern like d+ for one or more digits, and the tool hunts it through your sample text. Groups in parentheses remember pieces of each match, which is handy when you want to extract parts of an email or a date.
Notes & fun facts
Programmers have a running joke: «I had a problem, so I wrote a regex — now I have two problems». Regex is famously write-once-read-never, but even a half-hour with this tester usually means you will actually read your own pattern tomorrow.
Origin & history
Regular expressions were invented by Stephen Kleene in the mid-1950s as a mathematical model of finite automata. Ken Thompson put them into Unix in the late 1960s and then into grep (1973), which turned them from theory into everyday practice. JavaScript adopted Perl-style regexes in the 1990s.