Building a query string
Sometimes you don't have a full URL to build yet — just a set of parameters you need as a ?key=value&... string to append to something else, or to hand to fetch. Add them as key/value rows, or switch to JSON mode and paste an object — including one straight out of your code, like a filter or search state — and it converts directly, with array values expanding into repeated keys ({"tags":["a","b"]} becomes tags=a&tags=b) instead of needing to be flattened by hand.
For the full URL — protocol, host, path, and query together — see URL Builder. To go the other direction and pull parameters back out of an existing query string, see Query String Parser.
FAQ
Why can't I use a nested object in JSON mode?
A query string has no native concept of nesting — every value is ultimately just text. Flatten a nested structure into individual keys first (or JSON-encode the nested value yourself if that's genuinely what the receiving end expects).
Why does my value show a + instead of a space?
Query strings conventionally encode spaces as +, the standard application/x-www-form-urlencoded behavior — every URL parser decodes it back to a space correctly.