Regex Tester

Regex Tester

Type a pattern, see live match highlights, capture groups, and replace previews. JavaScript regex flavor with all flags. Common patterns are one click away.

Live highlight Capture groups Replace mode Pattern library

/ / 0 matches

g global i ignore case m multiline s dotall u unicode y sticky

Test string matches: 0

Email me at hello@example.com or finance@acme.co.uk for invoices, but route support@helpdesk.io to the team alias instead.

#	Range	Match	Group 1	Group 2	Group 3+

No matches yet.

How to read a regex

Slashes mark the boundaries: /pattern/flags. The pattern is what to match, the flags change how the engine matches. g finds all matches, i ignores case, m makes ^ and $ match line boundaries, s lets . match newlines.

Capture groups

Parentheses create groups. (\w+)@(\w+\.\w+) captures the local part as group 1 and the domain as group 2. Use them in Replace mode with $1 and $2. Named groups (?<name>...) are available with $<name>.

Common gotchas

• Backslashes need escaping in JS strings but not here, since you are typing the regex source directly.
• Without g, String.replace only replaces the first match.
• . does not match newlines unless you add s.
• Catastrophic backtracking can hang the engine on long inputs. If your pattern has nested quantifiers like (a+)+, simplify it.