Regex Tester

Regex Tester is a free browser-based tool that helps you test and debug regular expressions. It is part of ToolsMonk's developer tools collection, so you can finish the job without downloading software, creating an account, or jumping between multiple websites.

This tool is especially useful for workflows such as building and debugging a regex for form validation before shipping it, checking why a pattern isn't matching the strings you expect, and extracting and verifying capture groups for parsing tasks. Because it runs directly in your browser, you can use it on desktop, tablet, or mobile while keeping the process fast and easy for one-off tasks as well as repeat work.

Regex Tester is designed for people who want a practical, privacy-friendly workflow with instant results inside the larger ToolsMonk library.

Regex Tester lets you write a regular expression and instantly see what it matches in sample text, with live highlighting and a breakdown of captured groups. It turns the usually opaque process of crafting a regex into immediate visual feedback.

It uses the JavaScript (ECMAScript) regex engine — the one in every browser and Node.js — and exposes the common flags (global, case-insensitive, multiline, dotall) so the behaviour matches how your code will actually run the pattern. Toggling flags and watching the highlights update is the fastest way to understand why a pattern does or doesn't fire.

Everything runs locally, so your patterns and test strings, which often contain real data, never leave your browser. That makes it safe to paste production samples while debugging.

The most reliable way to build a complex pattern is incrementally: match a small fragment, confirm it highlights, then extend it, leaning on capture groups to extract exactly the substrings you need. For converting or generating expressions, pair this with the other ToolsMonk developer utilities.