Regex Tester

What is a Regex Tester?

A regex tester is an interactive online tool that lets you test regular expression patterns against text in real time. You can write a regex pattern, choose matching flags, and see all matches instantly highlighted in the input text. Each match displays its position, captured groups, and named groups, making it easy to debug and refine your regular expressions.

How to Use the Regex Tester

Enter your regular expression pattern in the Regex field. Type or paste the text you want to test in the Test Text field. The matches will appear automatically on the right side. Use the flags checkboxes to modify how the pattern is interpreted: enable g for global matching, i for case-insensitive matching, m for multiline mode, s for dotall mode, and u for Unicode mode.

Understanding Regex Flags

The global flag (g) finds all matches rather than stopping at the first one. The case-insensitive flag (i) makes the pattern match uppercase and lowercase letters interchangeably. Multiline mode (m) changes the behavior of the ^ and $ anchors so they match at the start and end of each line rather than the entire string. The dotall flag (s) allows the dot metacharacter to match newline characters. Unicode mode (u) treats the pattern as a sequence of Unicode code points and enables additional Unicode features.

Reading Match Results

Each match displays its starting index in the text, the matched value, and any captured groups. Capturing groups are shown as $1, $2, etc. based on their position in the pattern. Named groups appear with their specified names. The position range [start-end] shows where each capture begins and ends in the original text. The highlighted view makes it easy to see where matches occur visually. For a complete reference of regex syntax, check our Regex Memo cheat sheet.