Regex Tester: Test and Debug Regular Expressions Online
Regular expressions (regex) are one of the most powerful tools in a developer's toolkit for pattern matching and text manipulation. Our free online regex tester lets you write, test, and debug regular expressions in real time, with instant visual highlighting of matches and detailed information about captured groups.
The tool shows matches highlighted directly in your test string, making it easy to see exactly which parts of the text are matched by your pattern. Each match is listed with its index position and any captured groups, which is invaluable for understanding and refining complex patterns with parenthetical groups.
You can control the regex behavior using flags: "g" for global matching (find all matches), "i" for case-insensitive matching, "m" for multiline mode where ^ and $ match line boundaries, "s" for dotAll mode where . matches newlines, and "u" for Unicode support. Combining flags lets you fine-tune exactly how your regex operates.
Common regex use cases include validating email addresses, phone numbers, and URLs, extracting data from structured text, search-and-replace operations in code editors, parsing log files, and data cleaning. Master regex and you gain a skill that transfers across virtually every programming language and text editor.