Regex Matcher Online

Regex matcher, parser and validator for JavaScript patterns. Last updated July 28, 2026.

Formalint helps you test a regular expression against sample text before you paste the pattern into JavaScript, Node.js, frontend validation, log parsing or data cleanup code. The main matcher shows full matches, indexes, capture groups and named capture groups.

Open the Regex Matcher and Validator to test a pattern now, or use the notes below to choose safer patterns and test cases.

What to Test

A useful regex test should include values that should match, values that should not match, empty input, whitespace, long input and edge cases that are common in your real data. Testing only one happy-path example is how regex bugs reach production forms and parsers.

Example Pattern

This pattern extracts a log level and the remaining message from a simple application log line.

^(INFO|WARN|ERROR|DEBUG)\s+(.+)$

Regex Parser Notes

When people search for a regex parser, they usually want to understand what their pattern is capturing. In Formalint, each match displays capture groups separately, making it easier to confirm whether a parser extracts the intended fields rather than only matching the whole line.

Validation Notes

Formalint validates JavaScript regex syntax with the same browser engine that runs the test. Patterns written for PCRE, Python or .NET may need small changes before they behave the same way in JavaScript.

Related Formalint Pages

Use Regex Examples for common patterns, Regex Tester for live matching, Email Regex Validator for form checks, URL Regex Validator for link input, UUID v4 Regex for API IDs, Date Regex Validator for date strings and Regex Log Parser for capture group examples.

Frequently Asked Questions