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Regex Replace Tester

Test regex find and replace patterns directly in your browser. Preview replacements, capture groups, named groups, changed lines, match positions, flags, and before-after output.

Paste the text you want to search and replace. Everything runs locally in your browser.

Use JavaScript flags such as g, i, m, s, u, or y.

In JavaScript mode, use $1, $2, $&, $`, $', or ${name} for named groups.

Options

Tests JavaScript-style regex replacement behavior, including capture groups, named groups, replacement tokens, match positions, and changed lines.

Output

Regex replacement output will appear here.
Regex replacement testing happens directly in your browser. Your input text and patterns are not uploaded to a server.

Testing Regex Find and Replace Before Running It

Regex replacement is powerful, but a small pattern or replacement mistake can change more text than expected. Testing the pattern, replacement string, capture groups, and output first makes bulk edits safer.

This Regex Replace Tester lets you preview before-and-after text, inspect matches, check capture groups, review named groups, and copy the final replacement result without running it in your editor or script first.

Using the Regex Replace Tester

  1. Paste the text you want to search and replace.
  2. Enter a JavaScript-style regex pattern and flags.
  3. Enter the replacement text, including capture references if needed.
  4. Choose preview, result-only, match details, JSON, or Markdown output.
  5. Review changed lines and copy the final replacement output.

Common Regex Replace Use Cases

  • Testing capture group replacements such as $1, $2, and ${name}.
  • Renaming text patterns across logs, CSV exports, or code snippets.
  • Previewing changed lines before applying replacements in an editor.
  • Checking whether a global replacement matches too much text.
  • Debugging named groups and replacement tokens.
  • Creating before-and-after examples for documentation or scripts.

Example Regex Replacement

Pattern:     (?<name>[a-z]+)@(?<domain>[a-z0-9.-]+\.[a-z]{2,})
Replacement: ${name} [at] ${domain}

john@example.com -> john [at] example.com

Replacement Tokens Can Change the Result

JavaScript replacement strings support special tokens such as $1 for the first capture group, $& for the full match, and ${name} for a named capture group. This is useful, but it also means dollar signs in replacement text may need attention.

Use literal replacement mode or escape replacement text when you want the replacement string to be inserted exactly as typed.

Frequently Asked Questions

What does a Regex Replace Tester do?

It lets you test a regex pattern and replacement string, then preview the replaced output before applying it elsewhere.

Is this different from a Regex Tester?

Yes. A regex tester focuses on matching. This tool focuses on replacement output, changed lines, and replacement tokens.

Does it support named capture groups?

Yes. JavaScript-style named groups can be referenced in the replacement string with ${name}.

Why does replace all depend on the g flag?

In JavaScript regex, global replacement uses the g flag. The tool can add it for replace-all preview when needed.

Is my text uploaded anywhere?

No. Regex replacement testing happens directly in your browser.