# What is MCP (Model Context Protocol)?

Canonical page: https://agent-protocols-yxt.pages.dev/mcp
Checked against https://modelcontextprotocol.io/ on 2026-10-20. Uncertain items are marked unverified.

MCP is an open-source standard for connecting AI applications to external systems: data sources, tools and workflows. The official introduction compares it to a USB-C port for AI applications.

## Architecture

- **Host**: the AI application. It manages one client per server.
- **Client**: keeps one connection to one server.
- **Server**: a program that provides context. Local (stdio) or remote (Streamable HTTP).

## Server primitives

- **Tools**: functions the AI application can invoke (tools/list, tools/call).
- **Resources**: context data.
- **Prompts**: reusable templates.

Messages are JSON-RPC 2.0. The architecture page read describes protocol version 2026-07-28; earlier versions differ (check your SDK).

## MCP and A2A

MCP is agent to tool (vertical). A2A is agent to agent (horizontal). They are complementary. See https://agent-protocols-yxt.pages.dev/a2a-vs-mcp