Regex Tester
Test a regular expression against sample text with the matches highlighted in place, plus every capture group.
Free No signup Runs in your browser — nothing uploaded
What it does
Regex Tester operates on the text you paste, line by line, and shows the result as you type. Nothing is sent anywhere and there is no length limit beyond what your browser will hold.
When you need it
The kind of tidying that is tedious by hand and error-prone in a spreadsheet: a list pasted out of an email, an export with inconsistent casing, a column of addresses with duplicates in it.
Limits and caveats
Line endings are normalised, and leading and trailing whitespace is treated as significant unless the tool says otherwise. Nothing is stored: reload the page and the text is gone. Everything happens in your browser, so the file never leaves your device.
How to regex tester
- Write your pattern and pick the flags.
- Paste text to test it against.
- Matches highlight as you type, with the capture groups listed.
Frequently asked questions
- Which flavour of regex is this?
- JavaScript's, because it's your browser's own engine running the pattern. Most of it is shared with PCRE, but lookbehind support and named groups vary by language — check before pasting into Python or Go.
- Is my test data sent anywhere?
- No. That matters more than it sounds: debugging a pattern usually means pasting real log lines or real customer records, and those shouldn't go to a stranger's server.
- Do my files get uploaded?
- No. This tool runs entirely in your browser, so the file never leaves your device.