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MCP Explained walks through every message on the wire with live traces
MCP Explained is a free interactive guide that shows every Model Context Protocol message. The post reached 292 points on Hacker News.
Image: Runlayer
Why it mattersTeams adding MCP to their stack usually learn it from one example server. This guide shows the exact JSON on the wire for every step the client and server take.
A free online guide to the Model Context Protocol reached the Hacker News front page this week. The post has 292 points and 123 comments. The site is MCP Explained. It is written by Radek Wiliński and published by Runlayer, a New York company. Runlayer sells an MCP management platform. The guide is interactive. It walks through every message a client and server trade in MCP. Each step shows the exact JSON on the wire.
What the guide covers
The index names eight lessons on the core protocol. The handshake. JSON-RPC 2.0 as the envelope. The two transports: stdio for a local subprocess, and Streamable HTTP for a remote server. OAuth 2.1 and how a remote server rejects a request without a token. Then the methods: tools, resources, prompts and sampling. Each page carries a short summary, a fact table, and a trace of the exact messages sent in order.
The guide also covers newer parts of the spec. Tool search for servers with many tools. Elicitation, where a server asks the host app to show the user a form. Tasks, for work that takes longer than one request. Codemode. Each message in a trace has notes that explain the fields and when they were added to the spec.
The front page lists a short set of claims that the guide then proves. MCP sends JSON-RPC messages over stdin and stdout, or over one HTTP endpoint. Servers can talk back to the client. JSON-RPC is the envelope. MCP also sets the method names, capability negotiation, transports and auth.
What is new about it
MCP tutorials usually start by installing a server and showing a working tool call. This one works the other way. It names what a server has to answer when it gets each message. It also shows what changed between versions of the spec. One note points out that JSON-RPC batching was in an earlier spec and later removed. Another walks through the discovery flow a client uses to find the authorization server for a remote MCP server.
Who is behind it
The guide's own page names Runlayer as the publisher. Runlayer is a company in New York that sells, in its own words, an AI enablement, security and control platform. The company's site has a case study with Lemonade's security team. MCP Explained is free. There is no sign-up and no paywall. The site runs the trace itself in the browser.
The Hacker News submitter is Radek Wiliński, the author. The thread gathered 292 points and 123 comments within one day of being posted.
Source
- Primary source: MCP Explained: how the Model Context Protocol works, by Radek Wiliński, published by Runlayer.
- Discussion: Hacker News thread, 292 points.
- Publisher: Runlayer.
This item was written by an AI system from the linked source. Reveneau is responsible for what it publishes.
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