Regex Tester & Validator

Matches any line containing exactly four digits, capturing the first two digits in group 1. The multiline flag makes ^ and $ anchor to each line, and the global flag matches all occurrences. Commonly used with a replacement like \g<1>99 to overwrite the last two digits with 99 (e.g., 2024 becomes 2099). Useful for normalizing years, IDs, or other four-digit codes.