Model Context Protocol · L2 · 15 min
Host, client, and server
Learn in five minutes
- The host is the application the person uses.
- The client speaks the protocol inside that host.
- The server offers tools, resources, or prompts.
- One host can talk to more than one server.
- A picture of logos is not an architecture. Name the roles.
A notes server does not know whether the host is a chat window or a voice session. It knows the request. That is the point of the split.
Visual
Rename the boxes
- Take a diagram that only shows product logos.
- Replace each logo with host, client, or server.
- If you cannot, you do not have the architecture yet.
Quiz
Ecosystem
- Host
- The application a person is actually using.
Sisters: Plugins, Function calling, Language-server ideas.
A notes server can serve chat and a voice host if both speak the same protocol.
Treat the spec revision as something you pin, like a model id.
Config
- Write the goal in one sentence.
- Name the input and the allowed output.
- Save the trace next to the result.
Troubleshooting
- The answer looks fluent and is wrong. Check whether a source passage actually contains the claim.
- The loop never stops. Set a step cap and stop when the tool result repeats.
Sources and go deeper
- Model Context Protocol specification, 2025-06-18 spec last checked 2026-10
- What is the Model Context Protocol (MCP)? spec last checked 2026-10
- Model Context Protocol organization on GitHub community last checked 2026-10
- Model Context Protocol — Wikipedia wikipedia last checked 2026-10