Regex Tester

This tester compiles the pattern and flags with the browser's JavaScript RegExp engine, applies it to the supplied text, highlights each match, and reports its starting index and capture groups. Enter the pattern source without surrounding slash delimiters. Add g to collect every match; without it, JavaScript returns only the first match. Use the match count and indices to confirm repeated matches occur where expected.

• Prototype validation rules for identifiers, dates, log lines, or other constrained text.
• Extract repeated values such as email-like strings, ticket numbers, or named fields.
• Compare case-sensitive and case-insensitive behavior with i, or line anchors with m.
• Inspect capturing groups before moving a pattern into JavaScript or TypeScript code.

Pattern: \b([A-Za-z0-9._%+-]+)@([A-Za-z0-9.-]+\.[A-Za-z]{2,})\b. Flags: gi. Test text: "Contact Ada at ada@example.com or SUPPORT@EXAMPLE.ORG." The result is two highlighted matches. Capture group 1 contains each local part, while group 2 contains each domain. The g flag continues after the first match, and i makes letter case irrelevant.

This tool follows ECMAScript regular-expression syntax available in the current browser; PCRE, Python, .NET, and Java-specific constructs may fail or behave differently. A successful match proves only that the pattern matched, not that an email, URL, date, or other value is semantically valid. Ambiguous nested quantifiers can cause expensive backtracking on long input. Pattern evaluation and test text stay in the browser; still avoid sensitive production data on shared devices.