spakky-mcp 7.1.0

MCP client adapter that joins external MCP server tools into the Spakky Agent tool catalog

spakky-mcp

spakky-mcp is the Spakky Agent connector for external MCP servers.

It does one thing: connect MCP servers selected at run time and make their tools callable by the agent. It does not build MCP servers, and it does not expose an agent's own tools as an MCP server.

When to use it

Use this plugin when an agent service needs to attach MCP servers supplied by the developer, the service, or the end user:

• a configured company MCP server,
• a tenant-specific remote MCP endpoint,
• a user-connected GitHub/Linear/search MCP server,
• a per-run inline MCP server declaration.

The MCP server itself can be implemented with FastMCP, the official MCP SDK, or any compatible server implementation.

Install

uv add spakky-mcp
# or through the agent bundle
uv add "spakky[agent]"

Loading the plugin registers McpClient as IAgentRunnerFactory. Inbound adapters such as AG-UI and A2A can keep using the runner factory; MCP servers join the run through RunAgentInput.metadata.

v7 breaking change

spakky-mcp v7 removes the reverse "Agent tools as an MCP server" surface:

• removed MCPServer, MCPToolServer, McpToolServerConfig, build_agent_tool_server, serve_stdio, and the server registry modules,
• removed McpConfig.tool_server,
• removed Agent annotations whose only purpose was exposing local Agent tools as an MCP server.

The replacement path is intentionally one-way:

1. Build MCP servers with FastMCP, the official MCP SDK, or another MCP server framework.
2. Register allowed servers in McpConfig.servers or accept per-run inline declarations from user/service settings.
3. Pass selected servers through RunAgentInput.metadata["mcp"]["servers"].
4. Let spakky-mcp attach those external tools lazily through mcp_search_tools and mcp_call_tool.

Configure servers

Configured servers use the SPAKKY_MCP__ settings prefix.

export SPAKKY_MCP__SERVERS='[
  {"name": "weather", "transport": "stdio", "command": "weather-mcp-server"}
]'

Setting	Meaning	Default
SPAKKY_MCP__SERVERS	JSON array of external MCP server declarations	[]
SPAKKY_MCP__CONNECT_TIMEOUT_SECONDS	MCP connection timeout in seconds	30.0

Server fields:

Field	Meaning
name	Unique server name for one run. It cannot contain __.
transport	stdio or streamable_http
command, args, env	stdio server process command, arguments, and environment
url	streamable HTTP MCP endpoint
auth.headers	Static HTTP headers
auth.bearer_token_env	Environment variable containing a bearer token
auth.oauth_client_credentials	OAuth2 client-credentials token request config
call_timeout_seconds	Per-tool call timeout. Default 60.0

Runtime selection

At run time, pass configured server names or inline declarations through RunAgentInput.metadata["mcp"]["servers"].

from spakky.agent import IAgentRunnerFactory, RunAgentInput


async def run_with_user_mcp(factory: IAgentRunnerFactory, agent: object) -> None:
    run_input = RunAgentInput(
        state_id="run-1",
        instruction="answer with external tools",
        metadata={"mcp": {"servers": ["weather"]}},
    )
    async with factory.open_runner(agent, run_input=run_input) as runner:
        async for item in runner.run(run_input):
            ...

Inline server declarations support user self-service connections:

RunAgentInput(
    state_id="run-2",
    instruction="inspect issue status",
    metadata={
        "mcp": {
            "servers": [
                {
                    "name": "tenant-linear",
                    "transport": "streamable_http",
                    "url": "https://tenant.example.com/mcp",
                    "auth": {"bearer_token": access_token},
                }
            ]
        }
    },
)

Production services usually implement IMcpRuntimeServerResolver so a request carries stable connection IDs, while the server loads URLs and credentials from a DB or vault. Register that resolver as a Pod and bind it over the default resolver:

from spakky.core.application.application import SpakkyApplication
from spakky.core.application.plugin import Plugin
from spakky.plugins.mcp import IMcpRuntimeServerResolver


PLUGIN_NAME = Plugin(name="my-mcp-connections")


def initialize(app: SpakkyApplication) -> None:
    app.add(UserMcpResolver)
    app.container.bind_to_type(IMcpRuntimeServerResolver, UserMcpResolver)

Browser users should generally be allowed to add streamable_http endpoints, not arbitrary stdio commands.

AG-UI maps forwardedProps.mcp into the same metadata shape. A2A maps the data part mcp object into the same shape.

Lazy tool search

MCP servers can expose many tools. spakky-mcp does not push every external tool schema into the initial model request. The model sees only two MCP meta-tools:

Tool	Purpose
mcp_search_tools	Search tools available from the MCP servers attached to this run.
mcp_call_tool	Call one tool returned by mcp_search_tools.

External tool names are returned by search as <server_name>__<tool_name>. For example, weather server tool forecast becomes weather__forecast.

This keeps large MCP toolsets from polluting the model context while still letting the model discover and invoke the tools it needs. When mcp_call_tool requires human approval, the approval request names the selected external MCP tool and includes the selected arguments in metadata.

Development checks

Run package checks from this package directory:

uv run ruff format .
uv run ruff check .
uv run --project ../.. pyrefly check --disable-project-excludes-heuristics --min-severity warn --no-progress-bar --output-format min-text
uv run pytest

License

MIT License