Regex Tester

Write a regex, paste test text, and see every match highlighted in real time — plus capture groups and a replace mode.

Your pattern and test text never leave your browser.

How to use Regex Tester

  1. Enter your regular expression and any flags (like g, i, m).
  2. Paste the text to test against.
  3. Matches highlight automatically, with a list of captures below.
  4. Switch to “Replace” mode to preview replacements.

About this tool

Regular expressions are powerful but easy to get subtly wrong. The tester gives instant feedback — highlighting matches, listing capture groups, and showing errors as you type, with a replace preview for when you are building a substitution.

When to use it: building or debugging a regular expression before shipping it to code.

Frequently asked questions

Which regex flavour does this use?
The JavaScript engine built into your browser. Most common syntax is the same as in Python, PHP and other engines.
What do the flags mean?
g finds all matches, i ignores case, m makes ^ and $ match line starts and ends, s lets . match newlines, and u enables Unicode mode.
How do I match a whole word only?
Wrap it in word boundaries: \bword\b matches “word” but not “password” or “words”.
Can I test against multiple lines of text?
Yes — paste real multi-line content. With the m flag, ^ and $ anchor to each line instead of the whole text.
Why does my pattern show only one match?
Without the g flag only the first match is reported — add g to highlight every occurrence.
Is my pattern or test text stored?
No. Both stay in the page and never leave your browser.

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How to use Regex Tester

Paste your code, data, or URL into the Regex Tester input area. Select the appropriate mode or option, then process. The formatted or converted output appears clearly and can be copied or saved.

Practical benefits

Frequently asked questions

Is this tool free to use?
Yes. Regex Tester is fully free with no account or subscription required.
Does it upload my files?
No. All processing occurs locally within your browser session.
Can I use this for professional projects?
Yes, the tool is designed for both casual and professional use. Always verify critical outputs.