Regex Tester
Quickly test patterns, match text and preview replacements.
How to use the regex tester
- Type your regular expression into the pattern field and add flags if needed.
- Paste the text you want to search in the test area.
- Press Test to see the matches and capture groups, or type a replacement and press Replace.
- Review the result in the output and replacement areas.
- Start with a small pattern and grow it step by step, checking the matches after each change.
When it helps
- Debugging a regular expression before using it in code.
- Finding and replacing patterns across a block of text.
- Extracting values such as emails or dates from a document.
- Checking how capture groups behave.
- Extracting version numbers from a log file.
Frequently asked questions
Is my pattern and text private?
Yes. Everything is evaluated locally in your browser and never sent to a server.
What are the limitations?
The tester uses the JavaScript regular expression engine of your browser, so features from other engines may behave differently. Invalid patterns are reported rather than matched.
Which flags are supported?
You can add the common JavaScript flags such as case-insensitive, global, and multiline in the flags field.
Can I test replacements?
Yes. The replacement field shows how the text changes after the pattern is substituted.
Does it show capture groups?
Yes. The result area lists the matches and the captured groups for the current expression.
Why does my pattern find no matches?
The most common reasons are a typo in the pattern, a missing flag, or a pattern that expects characters that are not in the text. Start with a simpler fragment and confirm it matches before adding groups or anchors. The result area shows zero matches when nothing matches, so you can iterate quickly.