Regex Tester
Test and debug regular expressions instantly in your browser. Live match highlighting, match list, and flag controls. No signup required.
What is Regex Tester?
The Regex Tester lets you write, test, and debug regular expressions in real time. Paste your test string, enter your pattern, and matches are highlighted instantly as you type. Supports all standard JavaScript regex flags — global, case-insensitive, multiline, and dotAll.
Regular expressions are one of the most powerful and misunderstood tools in a developer's toolkit. Whether you're validating input, parsing log files, extracting data from strings, or writing a find-and-replace script, having an instant feedback loop dramatically speeds up the iteration cycle.
Everything runs in your browser — your patterns and test strings never leave your device. No account needed, no sign-up, no server upload.
How to use
Frequently asked questions
JavaScript's built-in RegExp engine, which follows the ECMAScript standard. Most common patterns are compatible across languages, with minor differences in advanced features like lookbehind.
Yes. Everything runs entirely in your browser. Your patterns and test strings are never sent to any server.
Invalid regex syntax (like an unclosed group or unsupported feature) will show an error message. Check for unescaped special characters — use a backslash to escape them.
The 's' (dotAll) flag makes the dot (.) character match newline characters as well as all other characters. Without it, dot does not match \n or \r.