Worcadian MCP Service

An MCP server, built with FastAPI, that wraps the Worcadian JSON-RPC game server API (https://worcadian.vercel.app/rpc, spec) as a set of MCP tools. Designed to be deployed as a Python serverless function on Vercel.

What it exposes

The service speaks MCP over Streamable HTTP at /mcp, with three tools:

MCP tool	Upstream JSON-RPC method	Arguments	Returns
check_wordlist	check	words: list[str]	{"WORD": true/false, ...}
gameday	gameday.current	none	{"min_day": int, "max_day": int}
results	board.results	game_day: int	{"num_submissions", "best_score", "submissions": [...]}

A plain GET /healthz route is also available for uptime checks.

How it works

• app/worcadian_client.py — a minimal async JSON-RPC client (httpx) for https://worcadian.vercel.app/rpc. Upstream error responses are raised as WorcadianRPCError.
• app/mcp_server.py — a FastMCP instance with the three tools above, each a thin wrapper around the client. Runs in stateless_http mode, since Vercel functions don't persist MCP session state between invocations, and with DNS rebinding protection explicitly disabled (that protection defaults to allowing only localhost/127.0.0.1 Host headers, which would reject every request once deployed on a real domain).
• app/server.py — the FastAPI app. It mounts the MCP app (which already serves /mcp by default) at the root, and wires its lifespan to start/stop the MCP session manager (required even in stateless mode, and not handled automatically by Starlette's Mount).
• api/index.py — the Vercel entrypoint; re-exports the FastAPI app.

Running locally

cd worcadian-mcp
python3 -m venv .venv && source .venv/bin/activate
pip install -r requirements-dev.txt
uvicorn app.server:app --reload

The MCP endpoint is then available at http://127.0.0.1:8000/mcp. Point an MCP client (Claude, Cursor, etc.) at that URL using its HTTP/Streamable-HTTP MCP server transport.

Testing

pip install -r requirements-dev.txt
pytest

Unit tests in tests/test_worcadian_client.py and tests/test_mcp_tools.py mock the upstream HTTP call (via respx), so they run offline.

tests/manual_smoke_test.py is not part of the automated suite — it makes real calls to the live Worcadian API (and optionally a deployed instance of this service) for a quick human sanity check:

python tests/manual_smoke_test.py
# or, against a deployed MCP server:
MCP_BASE_URL=https://your-deployment.vercel.app python tests/manual_smoke_test.py

Deploying to Vercel

cd worcadian-mcp
vercel deploy

vercel.json routes all requests to api/index.py via the Python ASGI runtime. No environment variables are required — the upstream API has no authentication.

After deploying, the MCP endpoint is https://<your-project>.vercel.app/mcp.

Out of scope

Only the three methods above are wrapped. The upstream API documents several other methods (board.submit, analyse, seedwords.check, checkin.*, the 14 Numbers game, etc.) that are not exposed by this service.