A regular expression (regex or regexp) is a sequence of characters that defines a search pattern. Regex is used to find, match, extract, or replace text based on patterns rather than exact strings.

How do I extract all email addresses from text?

Use the pattern [a-zA-Z0-9._%+\-]+@[a-zA-Z0-9.\-]+\.[a-zA-Z]{2,} with the Extract matches mode and the g (global) flag. This matches standard email address formats.

Regex Match Extractor & Replacer — Test & Debug Regex

Regular expressions are one of the most powerful tools in a developer's arsenal. This regex tester supports four modes: extracting all matches, extracting capture groups, find-and-replace, and filtering lines that contain matches — all running entirely in your browser with JavaScript's built-in regex engine.

Common Regex Patterns

\d+ — one or more digits
[a-zA-Z]+ — one or more letters
^start — line begins with "start"
end$ — line ends with "end"
\b\w+\b — any whole word
https?://\S+ — URLs
[\w.-]+@[\w.-]+\.\w{2,} — email addresses

Regex Flags

g — global: find all matches (not just the first)
i — case-insensitive
m — multiline: ^ and $ match line boundaries
s — dotAll: . matches newlines

Frequently Asked Questions

What regex engine does this use?

This tool uses JavaScript's built-in RegExp engine, the same engine used in Node.js and all modern browsers. The syntax follows the ECMA-262 specification.

How do I use capture groups?

Wrap parts of your pattern in parentheses: (\w+)@(\w+). Use the "Extract groups" mode to see each group's captures separately. In replace mode, use $1, $2, etc. to reference groups.

Regex Match Extractor & Replacer online

Test regex, extract matches and capture groups, and replace text — runs in your browser

Common Regex Patterns

Regex Flags

Frequently Asked Questions

What regex engine does this use?

How do I use capture groups?