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What Is MCP (Model Context Protocol)? Definition and Architecture
A definition of Model Context Protocol: the client-server model, the three primitives (resources, tools, prompts), and the two transports.
Direct answer
Model Context Protocol (MCP) is an open protocol that standardizes how AI applications connect to external context and tools through a client-server interface. A single MCP server, once built, works with any MCP-compatible client — instead of every application needing a custom integration for every data source and tool it wants to use.
Last reviewed 2026-08-29
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The client-server model
An MCP client (an AI application like an IDE assistant or a desktop app) connects to one or more MCP servers. Each server exposes a defined set of capabilities over a standard message format; the client doesn't need to know how the server is implemented internally, only that it speaks MCP.
This decouples tool authorship from application authorship: a database vendor can ship one official MCP server, and every MCP-compatible client gets database access without the vendor or the client author writing a bespoke integration for the other.
What a server can expose
- Resources — read-only or subscribable data addressed by URI, like a file or a database row.
- Tools — callable functions with a defined input schema that the model can invoke to take an action.
- Prompts — reusable, parameterized prompt templates for that server's domain.
How clients and servers connect
stdio runs the server as a local subprocess with no network exposure by default — the standard choice for local development and tools needing filesystem or process access.
Streamable HTTP exposes the server over a network endpoint for remote or multi-client deployments, and brings the usual web-service responsibilities — authentication, TLS, rate limiting — with it; the protocol does not enforce those for you.