LESSON 01 / 18·2 min readFoundation

MCP Foundations: Problem, Mental Model, and Boundaries

Must knowConcept lesson

Learning objectives

Understand the integration problem MCP solves.
Clearly distinguish the host, client, server, model, tool, resource, and prompt.
Decide when MCP is useful and when a normal API is sufficient.

Why MCP exists

Connecting AI applications to databases, APIs, files, and business services can require building a custom adapter for every integration. MCP provides an open protocol contract through which compatible hosts can discover and invoke server capabilities.

MCP itself is not a model, database, agent, or authorization system. It is a standard integration layer around existing backend capabilities.

Architecture at a glanceFollow the arrows to see how the parts connect.

Preparing the architecture diagram…

Read the full diagram flow

flowchart LR
  U[User] --> H[Host application]
  H --> M[Language model]
  H <--> C[MCP client]
  C <--> S[MCP server]
  S --> A[Existing API or service]
  S --> D[(Database)]

Core roles

Host: The user-facing AI application. It coordinates the model conversation and permissions.
Client: The protocol component inside the host. A separate client session may manage each server connection.
Server: Exposes tools, resources, and prompts.
Tool: An action or computation, such as lookup_order.
Resource: Readable context, such as documentation or a record snapshot.
Prompt: A reusable message template that a user can select.

Approach	Main purpose	Relationship with MCP
REST API	Application-to-application endpoints	An MCP server can reuse an existing REST service.
Model function calling	Providing callable schemas to a model	MCP standardizes discovery, transport, lifecycle, and capabilities.
RAG	Retrieving relevant knowledge to ground a prompt	MCP resources and tools can expose retrieval services.
Plugin	Product-specific extension	MCP provides an open protocol contract.

When to use it

When the same tools need to be reused across multiple compatible AI hosts.
When runtime tool discovery and structured schemas are useful.
When local tools or remote services need to be exposed through a consistent protocol.

When a normal API may be simpler

When there is only one fixed backend-to-backend call.
When an AI host or capability discovery is not needed.
When the team does not want to operate an additional protocol lifecycle.

Practical checkpoint

There is no need to rewrite an existing GET /orders/:id endpoint. The MCP handler can call the same order service. Authorization must be enforced at the service or handler boundary using authenticated user context; the model's instructions must not be trusted.

Revision note

MCP standardizes context and capability exchange. The host orchestrates execution; the model does not receive direct database access.

PAUSE & RECALL

Can you explain it without the notes?

MCP Foundations: Problem, Mental Model, and Boundaries

Use your own words. Explain an example and one limitation before checking the explanation.

Check your explanation

Learning objectives

CONNECT IT TO YOUR INTERVIEW

Turn this concept into a clear answer.