Skip to content
ToolsNest

Regular expression tester

Enter a pattern and test text to see every match, its position and its capture groups. Supports the i, m, s and u flags, with safeguards against runaway patterns.

Flags

Your text is processed in your browser as you type. It is not sent to ToolsNest servers or stored after you leave the page.

How to use the Regex Tester

  1. 1Type your regular expression.
  2. 2Choose flags (i, m, s, u).
  3. 3Paste test text and review the matches.

Supported formats and limits

  • Uses the JavaScript RegExp engine.
  • Up to 1,000 matches are shown; test text is limited to 100,000 characters.
  • Patterns are limited to 500 characters.
  • Invalid patterns show the engine's error message.

Common uses

  • Building a validation pattern for a form.
  • Extracting values with capture groups.
  • Debugging why a pattern does not match.

Frequently asked questions

Which regex flavour is this?

JavaScript. Syntax like lookbehind and named groups follows what your browser supports.

Related tools

JSON Formatter & Validator

Format, minify and validate JSON with line and column errors.

Open tool

Text Comparison

Compare two texts line by line and highlight the differences.

Open tool

Markdown Preview

Write Markdown and see the rendered result side by side.

Open tool