Model Context Protocol (MCP) Cheat Sheet

Primitives, transports and the client-server handshake

MCP standardises how an AI application connects to external context and tools, so one server works with every compatible client.

Category: MCP Difficulty: Advanced Version: 1.0 Updated: September 13, 2025 Author: Sabir

Server primitives

Primitive	Is	Controlled by
Tools	Actions the model may invoke	The model, at its discretion
Resources	Readable context — files, records, pages	The application, which chooses what to attach
Prompts	Reusable templates the user can trigger	The user, usually from a menu

Transports

Transport	Runs	Use for
`stdio`	As a local subprocess	Local tools, filesystem access, developer machines
`Streamable HTTP`	As a remote service	Shared and hosted servers
`SSE`	Remote, server-sent events	Legacy deployments; superseded by streamable HTTP

Handshake

Message	Direction
`initialize`	client → server: protocol version and capabilities
`initialize result`	server → client: its own capabilities
`notifications/initialized`	client → server: ready
`tools/list`	client → server: discover available tools
`tools/call`	client → server: invoke one
`resources/list, resources/read`	client → server: discover and fetch context
`prompts/list, prompts/get`	client → server: discover and expand templates

An MCP server is a trust boundary

Installing an MCP server grants it whatever access it asks for, and its tool descriptions become part of the model's instructions. Treat a third-party server the way you would treat a browser extension: read what it does, prefer least privilege, and remember that content it returns can itself contain injected instructions.

Code examples

Registering a local stdio server JSON

The client config that starts a server as a subprocess and speaks JSON-RPC over stdin/stdout.

{
  "mcpServers": {
    "filesystem": {
      "command": "npx",
      "args": ["-y", "@modelcontextprotocol/server-filesystem", "/srv/data"],
      "env": { "LOG_LEVEL": "info" }
    },
    "internal-api": {
      "type": "http",
      "url": "https://tools.internal.example/mcp",
      "headers": { "Authorization": "Bearer ${API_TOKEN}" }
    }
  }
}

FAQs

How is MCP different from plain function calling?

Function calling is per-application: you define tools inside your own code. MCP is a protocol, so one server works with every compatible client, and it adds resources and prompts alongside tools.

Is installing an MCP server safe?

Treat it like a browser extension. It runs with the access you grant it, and its tool descriptions become part of the model instructions. Prefer least privilege and read what it does first.