Regex Editor & Tester

Matches the query parameter named 'foo' in a URL when preceded by '?' or '&', optionally capturing its value after '=' up to the next '&' or '#' delimiter. Useful for extracting a specific query string parameter (e.g., 'foo=bar' from 'example.com?foo=bar&x=1'). Group 1 contains the parameter's value if present.