Support running fastmcp directly with an MCPConfig

src/fastmcp/cli/cli.py

@@ -291,16 +291,17 @@ def run(
 ) -> None:
     """Run an MCP server or connect to a remote one.
 
-    The server can be specified in three ways:
+    The server can be specified in four ways:
     1. Module approach: server.py - runs the module directly, looking for an object named 'mcp', 'server', or 'app'
     2. Import approach: server.py:app - imports and runs the specified server object
     3. URL approach: http://server-url - connects to a remote server and creates a proxy
+    4. MCPConfig file: mcp.json - runs the MCPConfig file directly
 
     Server arguments can be passed after -- :
     fastmcp run server.py -- --config config.json --debug
 
     Args:
-        server_spec: Python file, object specification (file:obj), or URL
+        server_spec: Python file, object specification (file:obj), MCPConfig file, or URL
     """
     # TODO: Handle server_args from extra context
     server_args = []  # Will need to handle this with Cyclopts context

src/fastmcp/cli/run.py

@@ -6,6 +6,7 @@ import sys
 from pathlib import Path
 from typing import Any, Literal
 
+from fastmcp.server.server import FastMCP
 from fastmcp.utilities.logging import get_logger
 
 logger = get_logger("cli.run")
@@ -142,6 +143,19 @@ def create_client_server(url: str) -> Any:
         sys.exit(1)
 
 
+def create_mcp_config_server(mcp_config_path: Path) -> FastMCP[None]:
+    """Create a FastMCP server from a MCPConfig."""
+    from fastmcp import FastMCP
+    from fastmcp.client import Client
+    from fastmcp.client.transports import MCPConfigTransport
+    from fastmcp.mcp_config import MCPConfig
+
+    mcp_config = MCPConfig.from_file(mcp_config_path)
+    client = Client[MCPConfigTransport](mcp_config)
+    server = FastMCP.as_proxy(client)
+    return server
+
+
 def import_server_with_args(
     file: Path, server_object: str | None = None, server_args: list[str] | None = None
 ) -> Any:
@@ -179,7 +193,7 @@ def run_command(
     """Run a MCP server or connect to a remote one.
 
     Args:
-        server_spec: Python file, object specification (file:obj), or URL
+        server_spec: Python file, object specification (file:obj), MCPConfig file, or URL
         transport: Transport protocol to use
         host: Host to bind to when using http transport
         port: Port to bind to when using http transport
@@ -192,6 +206,8 @@ def run_command(
         # Handle URL case
         server = create_client_server(server_spec)
         logger.debug(f"Created client proxy server for {server_spec}")
+    elif server_spec.endswith(".json"):
+        server = create_mcp_config_server(Path(server_spec))
     else:
         # Handle file case
         file, server_object = parse_file_path(server_spec)

tests/cli/test_run.py

@@ -1,10 +1,16 @@
+import inspect
+
 import pytest
 
 from fastmcp.cli.run import (
+    create_mcp_config_server,
     import_server,
     is_url,
     parse_file_path,
 )
+from fastmcp.client.client import Client
+from fastmcp.client.transports import FastMCPTransport
+from fastmcp.server.server import FastMCP
 
 
 class TestUrlDetection:
@@ -80,6 +86,49 @@ class TestFilePathParsing:
         assert exc_info.value.code == 1
 
 
+class TestMCPConfig:
+    """Test MCPConfig functionality."""
+
+    async def test_run_mcp_config(self, tmp_path):
+        """Test creating a server from an MCPConfig file."""
+        server_script = inspect.cleandoc("""
+            from fastmcp import FastMCP
+
+            mcp = FastMCP()
+
+            @mcp.tool
+            def add(a: int, b: int) -> int:
+                return a + b
+
+            if __name__ == '__main__':
+                mcp.run()
+            """)
+
+        script_path = tmp_path / "test.py"
+        script_path.write_text(server_script)
+
+        mcp_config_path = tmp_path / "mcp_config.json"
+        mcp_config_str = f"""
+            {{
+                "mcpServers": {{
+                    "test_server": {{
+                        "command": "python",
+                        "args": ["{str(script_path)}"]
+                    }}
+                }}
+            }}
+        """
+        mcp_config_path.write_text(mcp_config_str)
+
+        server: FastMCP[None] = create_mcp_config_server(mcp_config_path)
+
+        client = Client[FastMCPTransport](server)
+
+        async with client:
+            tools = await client.list_tools()
+            assert len(tools) == 1
+
+
 class TestServerImport:
     """Test server import functionality using real files."""