How do I reference capture groups in a regex replacement?

In JavaScript, use $1, $2, etc. in the replacement string to reference numbered groups. In Python, use \1, \2 with re.sub(). Named groups can be referenced with $ in JS or \g in Python.

How do I replace all matches, not just the first?

Enable the g (global) flag. Without it, only the first match is replaced. In Python, re.sub() replaces all matches by default.

Can I use regex replace to reformat dates?

Yes. For example, to convert YYYY-MM-DD to DD/MM/YYYY: pattern (\d{4})-(\d{2})-(\d{2}), replacement $3/$2/$1. The tester shows the reformatted output instantly.

What does $& mean in a replacement string?

$& in a JavaScript replacement string inserts the entire matched text. This is useful when you want to wrap matches rather than replace them, e.g. $& to bold all matches.

Can I test multi-line replacement?

Yes. Enable the m flag for multiline mode and the g flag for global replacement. You can test transformations across multiple lines of a pasted text block.

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Regex Replace Online — Preview Find and Replace

Test regex replacement operations before running them on real data or in production code. Enter your search pattern, your replacement string (with capture group references), and preview the output instantly — no risk of accidentally transforming the wrong content.

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Preview replacement output before using in code

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Supports capture group references in replacement

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Global replace with the g flag

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How to use this tool

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Enter your search pattern and replacement string. Use $1, $2 (or \1, \2 for Python) to reference capture groups in the replacement. Enable the g flag to replace all matches.

How It Works

Step-by-step guide to regex replace online — preview find and replace:

1
Enter your search pattern
Type the regex pattern that matches the content you want to replace. Use capture groups () for parts you want to preserve in the replacement.
2
Enter your replacement string
Type your replacement. Use $1, $2, etc. to insert captured group values. Use $& to insert the entire match.
3
Enable global flag if needed
Enable the g flag to replace all occurrences. Without g, only the first match is replaced.
4
Enter test string
Paste the text you want to transform.
5
Preview the output
See the replaced output in the results panel. Verify it looks correct before using the pattern in your code.