# Model Context Protocol (MCP)

An open protocol that standardizes how apps expose tools, data, and prompts to LLMs over a client/server link.

## Why the CCAR-P exam tests this

It is the backbone of P3 integration and candidates are expected to know its architecture and its security model cold.

## Definition

**MCP** standardizes the connection between an LLM application and external capabilities. The **host** (the AI app, e.g. Claude Desktop or an agent runtime) embeds one or more **clients**, and each client maintains a 1:1 connection to an **MCP server**. The server exposes three primitives: **tools** (model-invocable functions with side effects), **resources** (readable data the host attaches as context), and **prompts** (reusable templated workflows the user triggers).

The critical routing fact: the model decides which tool to call almost entirely from the tool's **`description`** and input schema, not from its name alone. A vague or misleading description causes wrong or missed tool calls, so descriptions are effectively prompt-engineering surface.

Servers should follow **least-privilege scoping** — expose only the tools a given task needs, with narrow parameters. Remote MCP servers authenticate via **OAuth / delegated tokens** tied to the acting user, never a shared static secret embedded in the server. Transport is JSON-RPC 2.0 over stdio (local) or streamable HTTP/SSE (remote).

## Exam trap

Tools are model-invoked while resources and prompts are app/user-controlled — treating all three as things the model freely calls is wrong, and assuming the model routes on tool name rather than description is the classic miss.

## Commonly confused with

- **mcp-vs-direct-api** — MCP is a standard integration layer; a direct API call is bespoke glue. Know when each is appropriate.
- **observability-tracing** — MCP moves the tool calls; tracing records them — the protocol is not itself the telemetry.

## Related

- mcp-vs-direct-api
- data-layer-acls
- observability-tracing

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Source: Claude Cert Prep — an independent, unofficial CCAR-P study resource (domain P3). Not affiliated with Anthropic.