RegEx Tester

What is a RegEx Tester?

A regular expression (regex) is a pattern used to search, match, and manipulate text. Regex is incredibly powerful but notoriously hard to get right — a small change can completely alter what a pattern matches. A regex tester lets you experiment with a pattern against sample text and see exactly what it matches, instantly.

Our RegEx Tester uses the JavaScript regular-expression engine, the same one that runs in every browser and in Node.js. As you edit your pattern or test string, it highlights all matches, shows how many were found, and breaks out the contents of each capture group.

How to Use the RegEx Tester

• Type your pattern between the slashes at the top
• Toggle flags like global, ignore case, and multiline as needed
• Enter or paste the text you want to test against
• Matches are highlighted in the preview and counted automatically
• Each match is listed with its position and any capture-group values

Understanding Regex Flags

Flags modify how a pattern is applied. The global flag (g) finds all matches rather than stopping at the first. Ignore case (i) makes the match case-insensitive. Multiline (m) lets the anchors ^ and $ match at line breaks. Dotall (s) lets the dot match newline characters. Unicode (u) enables full Unicode matching, and sticky (y) anchors the match to the current position.

Combining the right flags is often the difference between a pattern that works and one that silently misses matches. This tester makes flags easy to toggle so you can see their effect immediately.

Common Uses for Regex

Developers use regular expressions to validate input like emails and phone numbers, search and replace across files, extract data from logs and text, parse structured strings, and define routing or tokenizing rules. A reliable tester is essential for building and debugging these patterns with confidence. All testing happens locally in your browser, so your patterns and data stay private.