Free, runs entirely in your browser — no sign-up, no file upload to a server.
What does Regex Tester do?
It tests a regular expression against sample text, with live match highlighting, match positions, capture-group details, individual flag toggles (g, i, m, s, u, y), and a replace-mode preview.
How do I use it?
Enter your pattern and some sample text — matches are highlighted and listed as you type, with each match's position and capture groups shown below. Turn on "Replace mode" to preview a find-and-replace using
, $2, or
lt;name> in the replacement.
Which regex flavor does it use?
Your browser's native JavaScript RegExp engine. JavaScript's regex syntax differs in places from PCRE, Python's re, and other engines (for example, named groups use (?<name>…) syntax), so a pattern written for another language may need small adjustments here.
Can it get stuck on a pattern that matches an empty string?
No — zero-length matches (e.g. "a*") are specifically handled so the match scan always makes forward progress instead of looping.
Is my input sent anywhere?
Everything runs in your browser — nothing you type or paste is sent to a server.
How do I report a problem or request a feature for this tool?
Use the Contact / Feedback page — select "Regex Tester" as the related tool so we know exactly which tool you mean, then describe the bug or the feature you'd like to see.