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Regex tester & explainer

Regex Tester and Explanation Tool

JavaScript regular expressions only. Everything runs locally in your browser.

0 matches Valid regex

PatternNo slashes needed (enter the pattern only)

Performance (estimate)

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Run time

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Text

106 chars

Matches

Flags

giu

Enter a valid pattern and some text to measure.

FlagsToggle options

Active: giu

Tip: use g to see all matches; remove it to see just the first.

Test textPaste data or type freely

Highlighted matchesVisual preview

Contact: [email protected] Support: [email protected] Invalid: not-an-email@ Upper: [email protected]

MatchesIncludes capture groups

No matches found.

Max 500 matches rendered to keep things fast.

Regex explanationHuman-readable breakdown

Finds all matches. Looks for a match inside the input using JavaScript regex.

gGlobaliIgnore caseuUnicode

Breakdown

(?<user>

Named capturing group “user”.

[a-z0-9._%+-]

Character class (match one char from the set).

Repeat 1 or more times.

)

End of group.

Literal character.

(?<domain>

Named capturing group “domain”.

[a-z0-9.-]

Character class (match one char from the set).

Repeat 1 or more times.

Escaped literal “.”.

[a-z]

Character class (match one char from the set).

{2,}

Exactly 2 times.

)

End of group.

Quick tips

Use ^ and $ to validate the whole string.
Turn on g to see every match in the text.
Prefer [\\s\\S] if you need “any character” without relying on dotAll.

Common recipes

\\d+ — one or more digits
\\b\\w+\\b — whole words
^\\S+$ — non-empty, no spaces
^(a+)+$ — slow example (backtracking)

Privacy & engine

This tool runs entirely in your browser using the JavaScript regex engine. Your text and patterns are not sent to a server.

If you’re comparing against PCRE/.NET/RE2, behavior can differ (especially around lookbehinds, Unicode, and backtracking).

How it works

The tester compiles your pattern with the JS RegExp engine, runs it in a web worker, and streams matches plus a plain-language breakdown of each token.

Highlights, groups, flags, and JSON output come from the same run so they stay in sync.
Unsupported flags are disabled automatically; sticky and indices depend on your browser engine.

Quick examples

Hex color tokens

#[0-9A-Fa-f]{6}

#1e90ff

Capture ISO dates

(?<date>\\d{4}-\\d{2}-\\d{2})

date:2024-11-05

Use lazy quantifiers like *? to keep matches tight when text is long.

Mini FAQ

Does it support lookbehind?

Yes in modern browsers; older ones may fail to compile patterns with ?<= or ?<!.

Why do matches stop?

Rendering caps at 500 results to keep the UI responsive.

How do ^ and $ behave?

Without m they anchor the whole text; with m they anchor each line.