Regex tester
Try a pattern, list matches and groups, and replace.

Details
Type a pattern and a sample. The page lists matches and groups, and it can replace them. The sample stops at 20,000 characters and 200 matches so a bad pattern is less likely to freeze the tab. A pattern can still be slow.

Category: Developer
Page: /tools/regex-tester
Text: /tools/regex-tester.txt

Limits
Input is capped at 20,000 characters and 200 matches so a bad pattern cannot hang the tab forever. It can still be slow.

Steps
1. Enter a pattern and flags.
2. Paste the test text.
3. Read matches or apply a replacement.

Questions
Which engine?
The browser’s JavaScript RegExp.

What if the pattern is invalid?
The error message is shown and nothing is replaced.

Nothing is uploaded. Closing the tab drops the file.
The text stays here.