snowstorm-mcp-server

An MCP server for querying SNOMED CT clinical terminology via Snowstorm and Snowstorm Lite backends.

SNOMED CT is the world's most comprehensive clinical terminology, used in electronic health records across 80+ countries. This server exposes SNOMED CT lookup, search, validation, hierarchy navigation, and value set expansion through the Model Context Protocol (MCP), enabling AI assistants to work with clinical terminology directly.

Supports all SNOMED CT editions available on the connected backend (International, US, UK, AU, etc.). No user account is required when connected to a public Snowstorm instance.

This repository supports two related but distinct usage modes:

1. Hosted remote connector: run a public HTTPS MCP endpoint and connect Claude to it via the custom connector / Connector Directory flow.
2. Self-hosted or local usage: run the server yourself against your own Snowstorm or Snowstorm Lite deployment, including Claude Desktop and future MCPB packaging scenarios.

If you are preparing a hosted connector for Claude web/desktop/mobile, start with Hosted remote connector. If you want to run the server yourself against your own terminology backend, start with Self-hosted and local usage.

Hosted remote connector

Use this mode when you are operating a public MCP endpoint, for example https://your-domain.example/mcp, and want Claude to connect to it from Anthropic's infrastructure.

Hosted deployment (Docker)

Build and run the container:

docker build -t snowstorm-mcp-server .
docker run -p 8000:8000 --memory=512m --restart=unless-stopped snowstorm-mcp-server

Set --memory. Without a cgroup limit the container can grow until the kernel's global OOM killer fires, and that picks the largest process on the host — so a fault in this server takes the box down instead of just the container. With a limit, the container is killed alone and --restart brings it straight back.

The server starts in Streamable HTTP mode on port 8000 using the bundled config.docker-snowstorm.yaml (expects a local Snowstorm at http://localhost:8080). Mount your own config at runtime:

docker run -p 8000:8000 \
  -v /path/to/your/config.yaml:/app/config.yaml \
  snowstorm-mcp-server

For production, deploy behind an HTTPS reverse proxy or on a platform with automatic TLS (Cloud Run, Fly.io, Railway, etc.). For public-facing deployments, configure per-client rate limiting at the reverse proxy (IP-based). MCP 2026-07-28 removed protocol-level sessions, so the application-level per-session limit no longer applies to HTTP clients; the global limit still caps total backend load — see Performance guards below.

For remote MCP connector deployments intended for Claude web/desktop, the server enables CORS for https://claude.ai and https://claude.com on the Streamable HTTP endpoint by default. Override the allowed origin list with the SNOWSTORM_MCP_CORS_ALLOW_ORIGINS environment variable if needed using a comma-separated list.

Origin validation is on by default. A request to the MCP endpoint whose Origin header is present but not in the allow list is rejected with HTTP 403. This is what prevents DNS rebinding: a rebound page's POST still carries its real origin, because browsers attach Origin to every POST — including same-origin ones — per the Fetch Standard. Requests with no Origin at all, which is every non-browser MCP client, are unaffected.

That holds for all current browser engines. Firefox before 103 (July 2022) cou

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