Regex Tester
See matches live, and test replacements
Input
Refer to capture groups as $1, $2 and so on.
Result
Nothing entered yet
Enter a pattern and some test text — the results appear here.
Regular expressions are written by trial and error, and doing that inside your code means a rebuild for every attempt. Paste your sample text here and watch the matches move as you edit the pattern.
How to use
- 1 Enter the pattern — without the surrounding slashes.
- 2 Paste the text you want to test against.
- 3 Toggle the flags you need.
- 4 Add a replacement string to preview the substitution.
Frequently asked questions
What do the flags do?
g finds every match rather than stopping at the first, i ignores case, m makes ^ and $ match at line boundaries, and s lets the dot match newlines. Missing g is the single most common cause of "it only replaces once".
How do capture groups work?
Parentheses capture the matched portion. Refer to them as $1, $2 and so on in the replacement. Use (?:...) when you want grouping without capturing.
Why does my pattern hang the page?
Catastrophic backtracking — usually nested quantifiers like (a+)+ against text that nearly matches. The engine tries exponentially many combinations. Make the inner parts more specific or use non-greedy quantifiers.