Simon Willison’s Weblog

Introducing the Model Context Protocol (via) Interesting new initiative from Anthropic. The Model Context Protocol aims to provide a standard interface for LLMs to interact with other applications, allowing applications to expose tools, resources (contant that you might want to dump into your context) and parameterized prompts that can be used by the models.

Their first working version of this involves the Claude Desktop app (for macOS and Windows). You can now configure that app to run additional "servers" - processes that the app runs and then communicates with via JSON-RPC over standard input and standard output.

Each server can present a list of tools, resources and prompts to the model. The model can then make further calls to the server to request information or execute one of those tools.

(For full transparency: I got a preview of this last week, so I've had a few days to try it out.)

The best way to understand this all is to dig into the examples. There are 13 of these in the modelcontextprotocol/servers GitHub repository so far, some using the Typesscript SDK and some with the Python SDK (mcp on PyPI).

My favourite so far, unsurprisingly, is the sqlite one. This implements methods for Claude to execute read and write queries and create tables in a SQLite database file on your local computer.

This is clearly an early release: the process for enabling servers in Claude Desktop - which involves hand-editing a JSON configuration file - is pretty clunky, and currently the desktop app and running extra servers on your own machine is the only way to try this out.

The specification already describes the next step for this: an HTTP SSE protocol which will allow Claude (and any other software that implements the protocol) to communicate with external HTTP servers. Hopefully this means that MCP will come to the Claude web and mobile apps soon as well.

A couple of early preview partners have announced their MCP implementations already:

• Cody supports additional context through Anthropic's Model Context Protocol
• The Context Outside the Code is the Zed editor's announcement of their MCP extensions.