FastMCP Config Generator

FastMCPConfigGenerator

Factory for producing an MCP host configuration JSON from a stack dedicated to FastMCP.

Deterministic

Reads from environment and StackConfig; does not mutate the stack.

Source code in src/MCPStack/core/mcp_config_generator/mcp_config_generators/fast_mcp_config.py

@beartype
class FastMCPConfigGenerator:
    """Factory for producing an MCP host configuration JSON from a stack dedicated to FastMCP.

    !!! note "Deterministic"

        Reads from environment and `StackConfig`; does not mutate the stack.
    """

    @classmethod
    def generate(
        cls,
        stack,
        command: Optional[str] = None,
        args: Optional[List[str]] = None,
        cwd: Optional[str] = None,
        module_name: Optional[str] = None,
        pipeline_config_path: Optional[str] = None,
        save_path: Optional[str] = None,
    ) -> Dict[str, Any]:
        """Create the configuration mapping and optionally persist it to disk.

        !!! tip "Use with CLI"

            The `mcpstack build` command calls into this method.

        Args:
          stack: An `MCPStackCore` instance.
          command (str | None): Executable used to launch the server; defaults to the active Python.
          args (List[str] | None): Arguments for the command; defaults to `['-m', module_name]`.
          cwd (str | None): Working directory for the server process.
          module_name (str | None): Python module to run when using `-m`.
          pipeline_config_path (str | None): Path to the pipeline JSON produced by `stack.save()`.
          save_path (str | None): If set, write the config JSON here.

        Returns:
          dict: Configuration mapping suitable for MCP-compatible hosts.

        Raises:
          MCPStackValidationError: If `command` or `cwd` are invalid (FastMCP variant).
        """
        _command = cls._get_command(command, stack)
        _module_name = cls._get_module_name(module_name, stack)
        _args = cls._get_args(args, stack, _module_name)
        _cwd = cls._get_cwd(cwd, stack)

        if not shutil.which(_command):
            raise MCPStackValidationError(
                f"Invalid command '{_command}': Not found on PATH."
            )
        if not os.path.isdir(_cwd):
            raise MCPStackValidationError(
                f"Invalid cwd '{_cwd}': Directory does not exist."
            )

        env = stack.config.env_vars.copy()
        if pipeline_config_path:
            env["MCPSTACK_CONFIG_PATH"] = pipeline_config_path

        config = {
            "mcpServers": {
                "mcpstack": {
                    "command": _command,
                    "args": _args,
                    "cwd": _cwd,
                    "env": env,
                }
            }
        }
        if save_path:
            with open(save_path, "w") as f:
                json.dump(config, f, indent=2)
            logger.info(f"✅ FastMCP config saved to {save_path}.")
        return config

    @staticmethod
    def _get_command(command, stack) -> str:
        """Resolve `command` from explicit args, env, or sensible defaults."""
        if command is not None:
            return command
        if "VIRTUAL_ENV" in os.environ:
            venv_python = Path(os.environ["VIRTUAL_ENV"]) / "bin" / "python"
            if venv_python.exists():
                return str(venv_python)
        default_python = shutil.which("python") or shutil.which("python3") or "python"
        return stack.config.get_env_var("MCPSTACK_COMMAND", default_python)

    @staticmethod
    def _get_module_name(module_name, stack) -> str:
        """Resolve `module_name` from explicit args, env, or sensible defaults."""
        if module_name is not None:
            return module_name
        return stack.config.get_env_var("MCPSTACK_MODULE", "MCPStack.core.server")

    @staticmethod
    def _get_args(args, stack, module_name: str):
        """Resolve `args` from explicit args, env, or sensible defaults."""
        if args is not None:
            return args
        default = ["-m", module_name]
        value = stack.config.get_env_var("MCPSTACK_ARGS", default)
        return value if isinstance(value, list) else default

    @staticmethod
    def _get_cwd(cwd, stack) -> str:
        """Resolve `cwd` from explicit args, env, or sensible defaults."""
        if cwd is not None:
            return cwd
        return stack.config.get_env_var("MCPSTACK_CWD", os.getcwd())

generate(stack, command=None, args=None, cwd=None, module_name=None, pipeline_config_path=None, save_path=None) classmethod

Create the configuration mapping and optionally persist it to disk.

Use with CLI

The mcpstack build command calls into this method.

Parameters:

Name	Type	Description	Default
stack		An MCPStackCore instance.	required
command	str | None	Executable used to launch the server; defaults to the active Python.	None
args	List[str] | None	Arguments for the command; defaults to ['-m', module_name].	None
cwd	str | None	Working directory for the server process.	None
module_name	str | None	Python module to run when using -m.	None
pipeline_config_path	str | None	Path to the pipeline JSON produced by stack.save().	None
save_path	str | None	If set, write the config JSON here.	None

Returns:

Name	Type	Description
dict	Dict[str, Any]	Configuration mapping suitable for MCP-compatible hosts.

Raises:

Type	Description
MCPStackValidationError	If command or cwd are invalid (FastMCP variant).

Source code in src/MCPStack/core/mcp_config_generator/mcp_config_generators/fast_mcp_config.py

@classmethod
def generate(
    cls,
    stack,
    command: Optional[str] = None,
    args: Optional[List[str]] = None,
    cwd: Optional[str] = None,
    module_name: Optional[str] = None,
    pipeline_config_path: Optional[str] = None,
    save_path: Optional[str] = None,
) -> Dict[str, Any]:
    """Create the configuration mapping and optionally persist it to disk.

    !!! tip "Use with CLI"

        The `mcpstack build` command calls into this method.

    Args:
      stack: An `MCPStackCore` instance.
      command (str | None): Executable used to launch the server; defaults to the active Python.
      args (List[str] | None): Arguments for the command; defaults to `['-m', module_name]`.
      cwd (str | None): Working directory for the server process.
      module_name (str | None): Python module to run when using `-m`.
      pipeline_config_path (str | None): Path to the pipeline JSON produced by `stack.save()`.
      save_path (str | None): If set, write the config JSON here.

    Returns:
      dict: Configuration mapping suitable for MCP-compatible hosts.

    Raises:
      MCPStackValidationError: If `command` or `cwd` are invalid (FastMCP variant).
    """
    _command = cls._get_command(command, stack)
    _module_name = cls._get_module_name(module_name, stack)
    _args = cls._get_args(args, stack, _module_name)
    _cwd = cls._get_cwd(cwd, stack)

    if not shutil.which(_command):
        raise MCPStackValidationError(
            f"Invalid command '{_command}': Not found on PATH."
        )
    if not os.path.isdir(_cwd):
        raise MCPStackValidationError(
            f"Invalid cwd '{_cwd}': Directory does not exist."
        )

    env = stack.config.env_vars.copy()
    if pipeline_config_path:
        env["MCPSTACK_CONFIG_PATH"] = pipeline_config_path

    config = {
        "mcpServers": {
            "mcpstack": {
                "command": _command,
                "args": _args,
                "cwd": _cwd,
                "env": env,
            }
        }
    }
    if save_path:
        with open(save_path, "w") as f:
            json.dump(config, f, indent=2)
        logger.info(f"✅ FastMCP config saved to {save_path}.")
    return config

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