Friday MCP

MCP tools clients, transports and programmatic servers. Use the protocol APIs directly or let Friday Runtime own discovery, tool admission, diagnostics and lifecycle.

Distribution: friday-framework-mcp · Import: friday_mcp Python: 3.13.4+ · Status: alpha · License: MIT

Installation

python -m pip install "friday-framework-mcp==0.1.0a4"

Friday distributions use the same release version; keep internal Friday dependencies aligned.

Quick start: a local tools server and client

These two files use installed packages and an owned local subprocess. They require no network, credentials or model. Save this as server.py:

import asyncio
from friday_mcp.client.protocol import JSONValue
from friday_mcp.server import ModernStdioMCPServer, ToolCallResult

server = ModernStdioMCPServer()

async def echo(arguments: dict[str, JSONValue]) -> ToolCallResult:
    return ToolCallResult.text(str(arguments["message"]))

server.register_tool(
    {
        "name": "echo", "description": "Echo a message",
        "inputSchema": {
            "type": "object", "properties": {"message": {"type": "string"}},
            "required": ["message"], "additionalProperties": False,
        },
    },
    echo,
)

asyncio.run(server.serve())

Save this beside it as client.py, then run python client.py:

import asyncio
from pathlib import Path
import sys
from friday_mcp.client.stdio import StdioMCPClient

async def main() -> None:
    async with StdioMCPClient(
        name="demo", command=sys.executable,
        args=["-u", str(Path(__file__).with_name("server.py"))],
        protocol_profile="modern",
    ) as client:
        await client.list_tools()
        print(await client.call_tool("echo", {"message": "Hello from MCP"}))

asyncio.run(main())

Expected output: Hello from MCP. Keep server stdout exclusively for protocol messages. Always await client/server teardown. This is a tools-profile demonstration, not whole-protocol conformance.

Supported roles and profiles

Legacy HTTP+SSE is not the modern Streamable HTTP transport. Stdio configuration defaults to legacy compatibility; select modern or auto explicitly. HTTP requires a dated version and matching admission policy. The official mcp SDK is a development interoperability dependency, not Friday's production protocol implementation.

The optional server extra installs standalone HTTP server dependencies: python -m pip install "friday-framework-mcp[server]==0.1.0a4". full adds broader Friday integrations; extras do not activate remote peers.

Integrated Runtime/Chat configuration

tools.providers.mcp configures Friday as a client, not as a server. It is disabled by default. The client guide contains complete config.yaml examples for stdio and dated HTTPS profiles, remote/global opt-ins, environment credential references and canonical tool filters.

Runtime owns startup/reconnect discovery and registration. A required missing selected tool can stop startup even for an optional peer. Use public stop/start for integrated rediscovery. Programmatic clients also offer explicit generation-bound catalog refresh; it never replays a tool call and is not an automatic subscription.

Boundaries to understand

• These are bounded tools profiles. Modern clients do not advertise roots, sampling, elicitation or Tasks; interactive input_required continuation is unsupported. Integrated resources/prompts are not implemented. Do not claim complete MCP conformance.
• Modern text and structured JSON results are supported within dated rules. Unsupported media/resources and interactive continuation fail explicitly; no implicit URL/resource fetching occurs.
• Output-schema validation supports a bounded JSON Schema 2020-12 subset; external references, regex and unsupported constructs are rejected, not silently ignored.
• Default client ceilings include 1 MiB frames/catalog aggregate, 64 KiB tool results, four pending requests, 16 catalog pages and 256 tools. Runtime adds stricter admission/schema caps. User limits only lower the applicable modern ceilings.
• Remote clients require verified HTTPS and per-connection address policy. No redirects, environment proxies, TLS relaxation or automatic failed-call replay. Bearer credentials are explicit; OAuth discovery/login is not implemented.
• The modern HTTP server has one POST endpoint with explicit Host/Origin/bearer/TLS policy. It does not supply protocol sessions, a cache engine or OAuth login. Authentication and deployment remain application responsibilities.

See the guides for the full role/revision matrix, server lifecycle, protocol-specific errors, schema/result limits, security policy and controlled migration.

Development

Work from the monorepo root after the shared contributor setup. Run the focused suite:

uv run --no-sync pytest packages/friday-mcp/tests_mcp -q

Documentation and support

Client configuration · Server APIs · Protocol migration · Source · Issues · Contributing

License

MIT.