# Weather MCP

> Free, no-auth, public MCP (Model Context Protocol) server for multi-model
> weather data. Endpoint: https://weather.sillsengineering.com/mcp
> (streamable HTTP: single POST with JSON-RPC 2.0 per request; no SSE).
> Query 12 forecast/marine/ensemble/air-quality/archive weather models side
> by side and compute formally verified reductions (mean, std, min, max,
> spread, median, p10, p90, agreement) across models, time, or ensemble
> members on the server.

Key facts for agents:

- No API key, no signup, no auth headers. JSON-RPC 2.0 over HTTPS POST to /mcp.
- Two tools: `describe` (returns the full catalog of models, variables,
  dimensions; call it first) and `query` (variables[], location{lat,lon},
  time{start,end} as YYYY-MM-DD; optional models[] or "all", endpoint
  forecast|marine|air_quality|ensemble|archive, wind_speed_unit kmh|kn|ms|mph,
  timezone IANA, reduce{op,over,scale}).
- Models include GFS, ECMWF IFS, ICON, AROME France HD, ML models ECMWF AIFS
  and GraphCast, wave models EWAM/GWAM, GFS/ICON ensembles, CAMS air quality,
  and the ERA5 archive. 19 variables with units on every series.
- Responses use absolute unix-second timestamps, preserve nulls, and stamp
  provenance (model resolution, UTC offset, warnings for out-of-domain models).
- Cross-model `reduce` with op=spread or op=agreement is an uncertainty signal
  computed server-side; the reduction arithmetic carries formally verified
  (Kani-proven) contracts.
- Fair use: 30 requests/min/IP, 60 queries/hr/IP, and a global daily cap.
  HTTP 429 with Retry-After when exceeded — please back off and retry.
- GET /health returns liveness. GET or DELETE /mcp return 405 by design.
- Best effort service: free, no SLA. Not for safety-of-life decisions.
- Weather data by Open-Meteo (open-meteo.com).

## Docs

- [Landing page](https://weather.sillsengineering.com/): copy-paste setup for
  Claude Code / claude.ai / any MCP client, the two-tool overview, and a worked
  `query` example with real multi-model output and cross-model spread.

## Optional

- [Server manifest](https://weather.sillsengineering.com/.well-known/mcp.json):
  machine-readable MCP server card (server.json format).
- [Health](https://weather.sillsengineering.com/health): liveness endpoint.