Regex Tester
Test regular expressions in real time with live match highlighting, capture group details, and find-and-replace. Supports all JavaScript regex flags — no signup, no install, runs entirely in your browser.
How to Use the Regex Tester
Writing a Pattern
Type your regular expression directly into the pattern field. The tool uses JavaScript's RegExp engine, so any pattern that works in a browser console will work here. Matches are highlighted in your test string in real time as you type.
Flags
- g — global: find all matches, not just the first
- i — case-insensitive: match upper and lower case equally
- m — multiline:
^and$match the start and end of each line - s — dotAll:
.also matches newline characters
Capture Groups and Replace
Wrap part of your pattern in parentheses to create a capture group. The Match Details panel shows each group's value. In the Replace field, use $1, $2, … to reference groups, $& for the full match, or plain text for a literal replacement.
FAQ
What regex flavour does this tester use?
The tester uses JavaScript's built-in RegExp engine. It supports flags g, i, m, and s. Lookbehind, named capture groups, and Unicode escapes work in any modern browser.
How do I use capture groups in the replace field?
Use $1, $2, … to reference capture groups. $& inserts the full match. For example, replacing (\w+)\s(\w+) with $2 $1 swaps two words.
Why does my pattern match more than expected?
The global (g) and case-insensitive (i) flags are on by default. Toggle them off to restrict matching. Quantifiers like * and + are greedy — add ? after them for non-greedy matching.
Does this tool send my data to a server?
No. Everything runs entirely in your browser. Your regex patterns and test strings are never transmitted to any server.
Is there a limit on the length of the test string?
There is no hard limit. Very long strings with thousands of matches may cause a brief delay, but typical inputs — log lines, code snippets, API responses — are handled without issue.