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Regular Expression Tester & Debugger

Test and debug JavaScript regular expressions with real-time match highlighting, flag toggles, and capture group inspection.

  • 100% free
  • Files stay on your device
  • No sign-up, no watermark
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What is Regular Expression Tester & Debugger?

Build, debug, and test complex regular expressions against sample text. Features real-time match highlighting, full capture group breakdown, execution time measurement, and cheat sheets for regex tokens.

How to use Regular Expression Tester & Debugger

  1. 1

    Add your file or input

    Choose a supported file, drag it onto the upload area, or type/paste the data this tool works with.

  2. 2

    Adjust the options

    Pick the output format, quality, size or other settings the tool offers. Defaults work well for most files.

  3. 3

    Process and download

    Run the tool and save the result. Processing happens in your browser, so nothing is uploaded to a server.

Frequently asked questions

Which regex engine and dialect does this tester use?

It uses your browser’s native ECMAScript RegExp engine, supporting lookbehinds, named capture groups, unicode property escapes, and all standard regex flags (g, i, m, s, u, y).

How are capture groups and matches visualized?

Each matching match and indexed or named capture group is highlighted in alternating distinct colors with character index offsets displayed in an interactive breakdown table.

Does the tester protect against catastrophic backtracking (ReDoS)?

Yes. Regular expressions are tested within a guarded execution frame to catch runaway exponential backtracking patterns before they can freeze your browser.

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