Agentsadvanced5 min read

Model Context Protocol (MCP)

An open standard that lets models call tools and read resources exposed by any compatible server, across hosts.

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Before MCP, every agent framework had its own tool-calling convention. Model Context Protocol (MCP) is an open standard introduced by Anthropic in late 2024 that defines a single contract between a host (the model-bearing app) and one or more servers (tools, data sources, or context providers).

Three roles:

  • MCP Host — the application that owns the model. Examples: Claude Desktop, an IDE plugin, a chat product.
  • MCP Client — a connector inside the host. There is one client per server the host talks to.
  • MCP Server — a process that exposes tools (callable functions), resources (read-only data), and prompts (reusable templates) over JSON-RPC.

Why it matters:

  • Reusability. A server can be reused across compatible hosts. Transport support, protocol versions, authentication, and supported features must still match.
  • Security boundary. Hosts enforce consent and access policy. A local server is executable software; using MCP alone does not sandbox it or make its results trustworthy.
  • Composability. A host can mix local servers (filesystem) with remote servers (a hosted database) through the same protocol.

MCP messages use JSON-RPC. The standard transports are stdio for locally spawned servers and Streamable HTTP for remote servers; the older HTTP+SSE transport is retained only for backward compatibility.

MCP architecture. Host → Client → Server → data source. Servers are reusable across hosts.

Key takeaways

  • MCP defines host ↔ client ↔ server over JSON-RPC.
  • Servers expose tools, resources, and prompts.
  • It is the open standard that decouples agent frameworks from tool integrations.

Self-check

  1. What three primitives does an MCP server expose?

  2. What transport does MCP use?

Related concepts

References

  1. Model Context Protocol — Introduction — Anthropic

    Specification for connecting models to tools and data sources.

  2. Model Context Protocol — Transports — Model Context Protocol

    Current standard transports and HTTP+SSE compatibility guidance.

Last verified 2026-09-04.