TEXT PROCESSING / JAVASCRIPT REGEX

Regular Expression Tester

Explore JavaScript regular expressions with safe timeout handling, match highlighting, named and numbered capture groups, and live replacement previews.

Pattern & test data

Expression (without wrapping slashes)

Flags

Sample textReplacement template (supports $1, $&, $<name>)

Enter a pattern and click Test.

Match inspector

Highlighted matches

Match details & capture groups

#	Offset	Match	Groups

Replacement preview

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Regex flags and limitations

g finds all matches, i ignores case, m enables multiline anchors, s matches newlines with dot, u/v enables Unicode patterns, and y is sticky. This tester uses the browser's JavaScript regex engine; PCRE, Python and Java syntax may differ. The pattern runs in a dedicated worker with an execution time limit, protecting the UI from pathological backtracking. Very long inputs are limited for responsiveness.