About
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Regex Tester

Test expressions, flags and match positions

Usage guide and feature details

How do I test a regular expression?

Enter a pattern, flags and sample text to see matched values and indices immediately.

Regex Tester is a free online utility for development, testing, and everyday data tasks. It is designed to Test expressions, flags and match positions. No software installation or account is required.

Practical example and boundaries

Extract a status code from a log

Regex Tester uses the current browser JavaScript engine to show matches and capture groups for front-end validation, log extraction and text cleanup patterns.

Example input

Pattern: status=(\d{3})
Text: request completed status=200

Expected output

Full match: status=200
Capture group 1: 200

Limitations and cautions

JavaScript regex differs from PCRE, Java and Python. Catastrophic backtracking patterns can freeze a page, especially with long untrusted text.

Key features of Regex Tester

  • Process input instantly and spend less time switching between editors, terminals, and third-party apps.
  • Calculations run in your current browser by default, making the tool suitable for code, configuration, and debugging data.
  • Use essential features without registration, sign-in, or routine usage limits.
  • Works on desktop and mobile browsers with clear results that are easy to edit, copy, or download.

How to use Regex Tester

  1. Enter, paste, or select the content in the tool above, then adjust any available options.
  2. Choose the relevant action and Regex Tester will process and validate the input directly in your browser.
  3. Review the output, make any required changes, then copy the result or download the available file.

Common uses for Regex Tester

Use Regex Tester while building front-end pages, debugging APIs, reviewing configuration, preparing test data, or working on technical documentation. It helps you Test expressions, flags and match positions, which is useful for quick checks, one-off conversions, and repetitive development tasks.

Frequently asked questions about Regex Tester

Why does a regex from another language fail here?

Escapes, named groups, lookbehind and flags vary. This page follows browser JavaScript RegExp syntax.

Is Regex Tester free to use?

Yes. Regex Tester is free to use without registration and is designed to Test expressions, flags and match positions.

Is my input uploaded when I use Regex Tester?

This tool runs locally in your browser. Your input is never sent to our servers.