Query String Parser

About this calculator

A URL’s query string — everything after the “?” — carries key/value pairs separated by “&”, such as ?utm_source=email&page=2, and each value may be URL-encoded (spaces as %20 or +, special characters as percent-escapes) so it survives being embedded in a link. Parsing it means decoding those pairs back into readable key/value data.

Web developers use a parser like this constantly for debugging API requests, inspecting marketing UTM parameters, or checking what data a form actually submitted, and it also surfaces a common bug source: duplicate parameter names, which different frameworks handle inconsistently (keeping the first, the last, or turning it into an array). This tool parses a pasted query string into decoded key/value pairs and flags any duplicates it finds.