Connect to an MCP server

mistral.rs can act as an MCP client, connecting to one or more MCP servers at startup and merging their tools into the model’s available set.

MCP tools automatically use strict tool calling when the MCP server provides an input schema.

Starting with a config file

mistralrs serve --mcp-config mcp.json -m <model>

The MCP_CONFIG_PATH environment variable is an alternative to the flag.

Minimal config:

{
  "servers": [
    {
      "name": "filesystem",
      "source": {
        "type": "Process",
        "command": "npx",
        "args": ["-y", "@modelcontextprotocol/server-filesystem", "/tmp"]
      }
    }
  ],
  "auto_register_tools": true,
  "tool_timeout_secs": 30,
  "max_concurrent_calls": 4
}

Full schema: MCP config schema reference.

Transports

Three source.type values are supported:

• Process: launch the server as a subprocess and communicate over stdio.
• Http: connect over HTTP.
• WebSocket: connect over WebSockets.

Tool name prefix

Each server’s tools are exposed to the model as <prefix>_<tool>. The prefix is tool_prefix if set on the server entry, otherwise an auto-generated mcp_<uuid>. Separator is an underscore.

Concurrency and timeouts

max_concurrent_calls caps in-flight MCP calls. tool_timeout_secs is the per-call timeout. Http and WebSocket sources can override the timeout per-source.

Observability

MCP tool calls appear in agentic_tool_calls records and agentic_tool_call_progress streaming events with the prefixed name.