Test and debug a regular expression
See each match, group and replacement as you type, with the pattern explained in plain English.
- Runs on your device
- No sign-up
- Works offline after a visit
In a replacement, $1 is group 1, $<name> a named group and $& the whole match.
| # | Position | Match | Groups |
|---|
How the pattern reads
Code
How to test a regular expression
- Type the pattern and tick its flags.
- Paste the text you want to match against.
- Read the matches and the explanation, or copy the code for your language.
Questions
Is my text uploaded?
No. The pattern is compiled and run inside your browser, in a background worker. Nothing is sent to a server.
Why does the tester say a pattern takes too long?
Some patterns backtrack exponentially on text that almost matches, such as (a+)+$ on a long run of a. The tester stops a run after one second. Simplify the repeat, for example a+ instead of (a+)+.
Do JavaScript, Python and PHP differ?
Yes, in details. Python writes named groups as (?P<name>...) and has no \p{...} without a third-party module. PHP wraps the pattern in / delimiters and needs the u flag for Unicode matching. The code tabs show each change.
What do $1, $<name> and $& mean in a replacement?
$1 is the text of the first group, $<name> the text of a named group and $& the whole match. Each language writes the same replacement its own way.
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