Understanding Its Role First

A single MCP interaction typically goes through initialization, capability discovery, specific invocation, result return, and termination or continuation.

A single MCP interaction is usually not "connect and done." Instead, it involves initialization, capability discovery, specific invocation, result return, followed by continuation, termination, or error handling. Separating each step makes it possible to determine which layer a problem occurred at.

Understanding with an Example

When querying course materials, an application first agrees on a version and capabilities with the server, then discovers query tools, makes an invocation with the course ID, and checks the returned materials. If the ID does not exist, the application should handle the error rather than continue claiming to have read the materials.

Visual explanationUnderstand one usage process clearly
01Initialization

Agree on version and declare capabilities

02Capability Discovery

Query list of tools, resources, or templates

03Specific invocation

Request a capability with parameters

04Check the response

Continue, stop, or handle errors

This is a simplified process for understanding. Specific messages and versions need to be checked against the applicable specifications.

Going One Layer Deeper

  1. Initialization: Both parties agree on a protocol version they can use and declare their capabilities.
  2. Capability Discovery: The application queries the list of tools, resources, or prompt templates provided by the server.
  3. Specific Invocation: The application requests a capability along with its parameters.
  4. Result Inspection: The result may be materials, other data, or an error; the application then decides whether to continue, stop, or retry.

This flow helps in understanding the underlying logic, but specific message names, fields, and versions should be checked in the applicable specification. After the MCP server returns materials, the application also needs to decide whether to include the relevant content in the model's current context.

What It Does Not Explain

A successful initialization does not mean the required tool exists. A successful tool invocation does not mean the model has used the result. Task completion is not determined solely by protocol communication. Each conclusion requires corresponding evidence.

What to Learn Next

Sources

Content verified on 2026-09-13; this article is a pedagogical simplification; message flows for specific versions should follow the corresponding specification.