MCP configuration schema

When mistral.rs acts as an MCP (Model Context Protocol) client, it reads a JSON config describing servers to connect to.

Top-level fields

{
  "servers": [ ... ],
  "auto_register_tools": true,
  "tool_timeout_secs": 30,
  "max_concurrent_calls": 10
}

Field	Type	Default	Purpose
servers	array	required	List of MCP servers.
auto_register_tools	bool	required	Expose every tool from every connected server to the model. Has no serde default; omitting it is a parse error, so always set it (use true).
tool_timeout_secs	int	30	Per-tool-call timeout.
max_concurrent_calls	int	10	Cap on concurrent MCP calls.

Server entry

{
  "name": "filesystem",
  "source": { ... },
  "enabled": true,
  "tool_prefix": "fs",
  "bearer_token": "...",
  "id": "fs-1",
  "resources": ["file://**"]
}

Field	Type	Required	Purpose
name	string	effectively yes	Server name. No validation rejects omission (it defaults to an empty string), but the entry is unusable without it.
source	object	effectively yes	Transport configuration. Omission defaults to an empty-URL Http source, which will not connect.
enabled	bool	no (default true)	Disable a server without removing the entry.
tool_prefix	string	no (auto-generated mcp_<uuid>)	Prefix applied to tool names.
bearer_token	string	no	Optional bearer token.
id	string	no (auto UUID)	Stable identifier for the server.
resources	array	no	Resource URI patterns the server exposes, e.g. ["file://**"], used for resource discovery and subscription.

Transports, source object

Process (stdio)

{
  "type": "Process",
  "command": "npx",
  "args": ["-y", "@modelcontextprotocol/server-filesystem", "/tmp"],
  "env": { "KEY": "value" },
  "work_dir": "/path"
}

Field	Purpose
type	Literal "Process".
command	Executable to run.
args	Arguments.
env	Optional environment variables.
work_dir	Optional working directory.

HTTP

{
  "type": "Http",
  "url": "https://mcp.example.com",
  "headers": { "Authorization": "Bearer ..." },
  "timeout_secs": 60
}

Field	Purpose
type	Literal "Http".
url	Endpoint URL.
headers	Optional request headers.
timeout_secs	Optional per-source timeout.

WebSocket

{
  "type": "WebSocket",
  "url": "wss://mcp.example.com/ws",
  "headers": { ... },
  "timeout_secs": 60
}

Same fields as HTTP with a WebSocket URL.

Tool name prefix

Tools from a server with tool_prefix = "fs" are exposed as fs_read_file, fs_list_directory, etc. The separator is an underscore. Without tool_prefix, an auto-generated mcp_<uuid> prefix is used.

Example

{
  "servers": [
    {
      "name": "filesystem",
      "tool_prefix": "fs",
      "source": {
        "type": "Process",
        "command": "npx",
        "args": ["-y", "@modelcontextprotocol/server-filesystem", "/srv/agent-workspace"]
      }
    },
    {
      "name": "github",
      "source": {
        "type": "Http",
        "url": "https://mcp.github.example.com",
        "headers": {
          "Authorization": "Bearer xxx"
        }
      }
    }
  ],
  "auto_register_tools": true,
  "max_concurrent_calls": 8,
  "tool_timeout_secs": 45
}

Pass it on the CLI:

mistralrs serve --mcp-config mcp.json -m Qwen/Qwen3-4B

The same path can be supplied via the MCP_CONFIG_PATH environment variable.