Understanding Its Role First

MCP services can provide tools, resources, and prompt templates according to conventions; what specifically is available depends on the service implementation.

MCP services can provide several categories of capabilities according to shared rules: Tools, Resources, and Prompt Templates. They address different problems; a service declaring support for a category does not mean it necessarily provides the specific item you need.

Understanding Through an Example

A course materials service might provide a tool for querying materials by course number, a course catalog resource, and a lesson preparation prompt template that accepts course numbers as parameters. An application should first discover capabilities, then verify the specific one actually needed.

Visual explanationFirst, clarify what the service provides
01Tool

Request an operation and get the result or error

02Resource

Read content by identifier

03Prompt template

Get a template with fillable parameters

The three types of capabilities have different responsibilities. Whether they are provided and who calls them depends on the specific application and service.

Going a Layer Deeper

  • Tool: Requests a specific operation, returns data or an error—for example, querying materials by course number.
  • Resource: Reads content by identifier—for example, reading a course catalog or a document.
  • Prompt Template: Retrieves a request template with selectable and fillable parameters; reading the template itself does not automatically generate an answer.

Across different applications, the interface may vary in terms of who initiates the call and who decides to include the result in context. During usage, separately record "what was discovered," "what was actually called," and "what was returned."

What It Cannot Tell You

Capability discovery does not guarantee successful invocation, and successful invocation does not guarantee task completion. When a tool returns course materials, it only proves that the read operation succeeded; whether the materials are complete or the generated lesson plan is suitable still requires additional verification.

What's Next to Learn

References

Content verified on 2026-09-13; capability names and invocation methods may change with protocol versions and application implementations.