sling

Go's net/http makes you assemble every HTTP request by hand. Sling is a small library that makes building and sending those requests less tedious. Instead of manually constructing http.Request objects, setting headers, encoding query parameters, and parsing responses, Sling gives you a chainable builder pattern. A Go equivalent of Python's requests library, but lighter.

MIT license, Go. The API is clean: sling.New.Base(url).Get(path).QueryStruct(params).ReceiveSuccess(response). Supports JSON encoding/decoding, form data, custom headers, and base URL composition. No external dependencies beyond the standard library.

Fully free. It's a library. Install it with go get, use it in your code. No service, no hosting, nothing to pay for.

The catch: this is a mature-but-quiet project. The Go standard library's net/http is already good. Sling saves typing but doesn't add capabilities. If your team has strong opinions about minimizing dependencies, the standard library does everything Sling does with more code. And for complex API clients, you might want a full SDK generator like OpenAPI instead of a request builder.