Regex Tester Online
A real-time workspace for developers to write, evaluate, and test regular expressions. Instantly highlight matches, analyze capture groups, and check for backtracking issues.
How Does the Regex Tester Work?
Our online regex tester runs regular expressions directly inside a client-side environment using background Web Workers. This ensures your test text is processed instantaneously without any communication with a backend server, securing your private keys, email addresses, or client files.
When you enter a pattern in the pattern input, the tool's parser tokenizes it into an Abstract Syntax Tree (AST). If there's a syntax error, it's flagged with an error banner immediately, explaining the fix. Otherwise, the matching worker executes and paints match highlights on your string.
Understanding Regex Flags
Flags modify how the regex matching engine traverses the test string:
- g (Global): Find all matches in the text rather than stopping after the first match.
- i (Case-insensitive): Ignore letter case differences (e.g.
[A-Z]behaves like[A-Za-z]). - m (Multiline): Makes boundary anchors
^and$match the start and end of individual lines instead of the entire text string. - s (Single line / Dotall): Allows the dot token (
.) to match newline characters as well.
Explore Other Interactive Utilities
Check out other specialized checkers in the suite: