Query String Parser

A query string parser converts the part of a URL after the question mark into structured data. The query string q=json+parser&page=2 becomes the object {"q":"json parser","page":"2"}, with each key and value URL-decoded so a plus sign turns back into a space and %2F turns back into a slash. This tool parses in that direction, and also runs the reverse: it builds a correctly encoded query string from a JSON object of key-value pairs.

Query strings look simple until repeated keys and array syntax appear. The same key can occur more than once, as in tags=react&tags=laravel, and many frameworks encode arrays and nested objects with brackets, such as tags[]=react or filter[color]=red. A parser has to decide whether those become an array, a nested object, or a last-value-wins scalar, and different back ends disagree. This tool exposes those choices so the JSON you get matches the system that produced the URL, and the query string you build matches the system that will read it.

Everything runs in your browser. Parsing, decoding, and encoding are done in JavaScript, so nothing is uploaded, logged, or stored. That is worth having for URLs that carry session tokens, tracking parameters, or signed values in the query, because those never leave your machine, and the tool keeps working offline once the page has loaded.

Query strings have less of a standard than their ubiquity suggests, and repeated keys are where implementations diverge. Given a=1&a=2, some frameworks return an array, some the first value, some the last. Bracket notation such as a[]=1&a[]=2 is a PHP convention that many libraries adopted and no specification defines, so a server that does not know it will read the literal key a[]. Both forms are shown here so you can see what a given string actually contains. Encoding is the other half: a space may be a plus sign or %20 depending on whether the string came from a form submission or from a URL path, and the two are decoded differently. An ampersand inside a value has to be encoded, or it silently becomes a parameter separator.