Roundtrip

Roundtrip teaches how the web actually works under the hood, without needing a single line of network code or even an internet connection. You assemble an HTTP request piece by piece — pick a method, set the path, add headers, write a body — and then watch the whole request-response round trip play out step by step, so the invisible machinery behind every web page becomes something you can actually see.

It's built as a hands-on learning tool, not a real network client — everything is a clear, offline simulation designed to teach, running against a small simulated server with real endpoints to explore. As you build a request, Roundtrip shows you the raw HTTP message that would go out, and simulates a matching response: status line, headers, and body, with the status code explained in plain language so you finally know your 200 from your 404 from your 500. A guided set of lessons walks through the core ideas — methods, status codes, headers, request and response structure — each with a small challenge to build the right request for a goal, and a hint if you get stuck.

An Endpoints map lays out exactly what the simulated server understands, so you're never just guessing at paths — tap one to see what it does, or jump straight into the sandbox with it loaded. A tappable reference keeps common methods, status codes, and headers a tap away, each with a real example. Save any request worth remembering to your history, and track your progress with milestones as you explore more of what HTTP can do.

Because it's a controlled simulation, it's a safe, clear place to build a real mental model of HTTP before touching actual tools.

Everything runs on your device: no account, no connection, no ads. Just requests, responses, and the web explained.