Chapter C55 · Interactive Course
MCP connects an application to capabilities
Host, client, server, messages, versions and mutual support.
Core Learning Concept
Trace the protocol exchange across host, client, and server components. Match request identifiers, separate capability discovery from execution, and verify protocol version specifications before diagnosing runtime connection lifecycle behaviors accurately.
What You’ll Learn in This Chapter
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One program asking another for something
Follow a request from one program to another and name the address, the request, the response and what each layer establishes.
A network request is one program asking another for data or actions. The client initiates the inquiry while the server responds. Addresses locate machines, ports route to specific programs, and HTTP standardizes message formats across networks.
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MCP standardizes an integration boundary
Explain the reusable connection contract between an AI application and a server.
Model Context Protocol, or MCP, defines an interface for applications to exchange context and capabilities with servers. It standardizes parts of the integration rather than making the underlying service more accurate or trustworthy. Follow what information crosses the boundary and which operation the service actually performs.
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The host is the user-facing application
Locate the application coordinating a connected task.
The host is the application coordinating the user experience and its MCP clients. It decides how server capabilities and results are used within the AI workflow. A host may connect to several servers. Being connected does not mean every server receives all conversation content or every offered tool is automatically used.
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The client connects on the host’s behalf
Identify the connector between host and server.
An MCP client is the component that communicates with a server on the host’s behalf. Hosts commonly manage a client for each server relationship. The client handles the protocol exchange; it is not the language model itself. Version and capability handling determine which exchanges that relationship supports.
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The server exposes capabilities
Identify the service publishing usable tools or context.
An MCP server is a program exposing capabilities through the protocol. It may run locally or remotely and may call other software behind the interface. “Server” describes its role, not necessarily a separate physical machine. Inspect its implementation and access to understand what an offered operation can do.
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JSON-RPC carries named messages
Recognize a method, parameters and request identifier.
JSON-RPC messages specify method names, parameters, and unique request IDs. Responses repeat that ID to correlate answers accurately with calls. Valid syntax formatting is distinct from whether the backend operation succeeds or fails.
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Versions define the conversation rules
Explain why a tutorial's protocol era matters.
Protocol specifications change across versions. Early MCP versions required explicit initialization handshakes, whereas newer revisions utilize per-request metadata. Always confirm version compatibility between client and server before troubleshooting apparent communication failures.
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Capabilities must be supported
Separate a documented feature from support at both ends.
A specification can describe features that a particular client or server does not implement. Check declared support, protocol version, and any extension requirements before relying on a capability. The relevant question is whether this complete connection supports the needed operation, not whether the feature exists somewhere in the standard.
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Label a connected task
Identify every role and message in a supplied notes-server trace, and explain which version assumptions it uses.