Regex Tester - Live JavaScript Regex Debugger

Test JavaScript regex patterns locally with live highlights, flags, match counts, and capture groups. Debug sample text in your browser with no uploads.

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Matches

2 matches
[email protected]\[email protected]\nnot-an-email

Capture Groups

#IndexMatchGroups
10[email protected]none
221[email protected]none

How to Use

  1. Type or choose a regular expression.
  2. Paste the sample text you want to test.
  3. Toggle flags such as g, i, or m.
  4. Review highlighted matches, match count, and capture groups.
  5. Copy matches or keep refining the pattern.

Note: The first version uses JavaScript RegExp, which differs from PCRE, Python, and other regex flavors.

Core Features

  • Live JavaScript Regex Testing: Type a regex pattern and sample text to see matches instantly.
  • Flag Toggles: Switch common g, i, m, s, and u flags quickly.
  • Capture Group Inspector: Review capture groups for each match to debug parsing logic.
  • Local Text Debugging: Logs, payloads, identifiers, and snippets stay in your browser.
  • Useful Presets: Start with common patterns for email, URL, UUID, whitespace, and log levels.

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Calculation Logic

The tool uses the browser's JavaScript RegExp engine locally:

  • The pattern is compiled into a JavaScript regular expression.
  • Flags change case sensitivity, multiline behavior, global matching, and more.
  • Capture groups expose specific parts inside each match.
  • Input length is capped to reduce the risk of slow patterns freezing the page.

FAQ

Is my sample text uploaded?

No. Matching runs locally in your browser, and sample text is not uploaded to a server.

Which regex flavor does this use?

The first version uses JavaScript RegExp. It does not emulate PCRE, Python, RE2, or other engines.

How do I see capture groups?

After a match is found, capture groups are listed per match so you can inspect each parenthesized submatch.

Why does my regex work elsewhere but not here?

Regex syntax varies by language and engine. This tester follows JavaScript regex behavior.

Can a regex freeze the page?

Very complex patterns can be expensive. The tool limits input length and reports errors or boundaries in the UI.