Regex Tester

The Regex Tester is a browser-based tool that lets you write, test, and debug regular expressions against any input string in real time. As you type your pattern, matches are highlighted instantly, capture groups are extracted and displayed, and flag combinations like global, case-insensitive, and multiline are fully supported — giving you immediate visual feedback without needing to spin up a local environment or write throwaway test scripts.

For developers, regular expressions are a daily necessity — from validating email addresses and parsing log files to extracting tokens from structured text. But regex syntax is notoriously tricky, and subtle mistakes can cause silent failures or unexpected behavior in production. Having a dedicated, interactive tester removes the guesswork, making it faster to build correct patterns and easier to understand why a particular expression does or doesn't match.

To use the tool, paste or type your target string into the input field, then enter your regular expression pattern in the pattern field. Matches are highlighted in the input text as you type, and any named or unnamed capture groups are shown in a structured breakdown below. You can toggle common regex flags — such as g (global), i (case-insensitive), m (multiline), and s (dotAll) — using the provided flag controls, and the results update immediately with each change.

The output panel shows every match found, its index position within the string, and all captured groups with their respective values. This makes it straightforward to verify not just whether a pattern matches, but exactly what it captures — which is especially important when building patterns used in code for data extraction or transformation.

A few edge cases to be aware of: patterns with the global flag (g) will return all matches, while omitting it returns only the first. Lookaheads, lookbehinds, and Unicode property escapes (\p{}) are supported in modern JavaScript engines, but behavior may differ across environments. If your pattern contains a syntax error, the tool will surface the error message immediately so you can identify and fix it without ambiguity.