Matches highlighted
Tested in November 2026. Matches, groups, named groups, flags, replacement, errors, Unicode patterns and the 1000 match limit were tested with sample patterns.
How to test a regular expression
- Type your pattern in the top box without the slashes.
- Choose the flags you need. Global is on by default so every match is found.
- Paste the text to test. Matches are highlighted and listed with their position and groups.
- Add a replacement if you want to test a replace. Use $1, $2 and $<name> for groups.
- Click Copy expression to copy the pattern with its flags.
Tips for better results
- Click Load an example to see groups and a replacement at work.
- Turn on the unicode flag to use patterns such as \p{L} for letters in any language.
- Turn on multiline to make ^ and $ work on each line.
- Build the pattern in small steps and watch the highlight change.
Limits to know about
- The tester uses the JavaScript regular expression engine. Other languages such as Python or PHP can behave differently.
- A pattern with heavy backtracking on long text can freeze the page for a while.
- Only the first 1000 matches are used and the table shows the first 200.
- Hindi words that use vowel signs can split in the middle with \p{L}. Add \p{M} to include the signs.
Privacy
Your pattern and text stay in your browser and are not sent to ToolsRiver.
Frequently asked questions
What does the g flag do?
It finds all matches instead of only the first one.
How do I use groups in a replacement?
Write $1 for the first group, $2 for the second and $<name> for a named group.
Why do I see an invalid pattern message?
The pattern has a syntax problem, such as a bracket that is not closed. The message says what is wrong.
Can I test a pattern for Python?
You can try it, but features differ. Check the result in your own language.
Is it free?
Yes, with no sign-up.
About this tool
ToolsRiver Regex Tester shows matches, groups and replacements live for JavaScript regular expressions. It runs in your browser.