Regex Tester Online

Regex, short for regular expression, is a pattern language used to find, match, validate, extract, or replace text. Regular expressions are commonly used for input validation, log parsing, search-and-replace, data extraction, routing rules, and other tasks where text follows a recognizable pattern.

Build the pattern in small pieces, test it against examples that should match and examples that should not, and check how flags or groups change the result. Avoid relying on a complex expression before testing edge cases. The tester above lets you try the pattern against real text before moving it into application code.

In many regular-expression flavors, $ is an anchor that matches the end of a string or, depending on flags and the regex engine, the end of a line. It normally matches a position rather than consuming a character. The exact behavior can vary with multiline settings, so test the expression with the same flags you plan to use.

Run the expression against representative test text and inspect the matched ranges, capture groups, and unmatched cases. Visual highlighting makes it easier to understand what the pattern is doing than reading the expression alone. Use the tester above to inspect matches while you edit the pattern and flags.

In JavaScript and several other regex implementations, the s or dotAll flag allows the dot metacharacter to match line-terminator characters as well as other characters. Without dotAll behavior, a dot normally does not cross line breaks. Test multiline input to confirm the behavior expected by your target regex engine.

Use the same pattern, flags, and representative input that your JavaScript code will receive, then check matches, groups, replacements, and edge cases. Testing the expression independently makes it easier to separate a regex problem from surrounding application logic. The tester above is designed around this quick verification workflow.