Rain Check
A remote MCP server that answers whether an Australian field-service job can beworked at a place on a day, for a given trade, from live forecast, daylight andpublic holiday data.
Live: https://rain-check-mu.vercel.appMCP endpoint: https://rain-check-mu.vercel.app/mcpOpenAPI: https://rain-check-mu.vercel.app/openapi.jsonHealth: https://rain-check-mu.vercel.app/health
Connect it
claude mcp add --transport http rain-check https://rain-check-mu.vercel.app/mcp
Any MCP client that speaks Streamable HTTP can use the same URL. It is POSTonly: the server is stateless, so GET and DELETE answer 405 by design.
For anything that does not speak MCP, the identical operations are at/v1/<operation> and described by /openapi.json, which is generated from thesame constants the MCP tools use so the two cannot drift.
Run it locally
npm install
npm run typecheck # tsc, no emit
npm run smoke # every operation against the real upstreams
npm run smoke:mcp # every endpoint over a real node:http server
npm run smoke:live -- https://rain-check-mu.vercel.app # the deployed server
npm run adversarial -- https://rain-check-mu.vercel.app # tries to break it
npm run prove -- https://rain-check-mu.vercel.app # independent evidence
There are no mocks anywhere. The point of these is to catch an upstream changingshape, and a mock never will.
npm run adversarial is the one that finds things. It throws nonsense ranges,hostile strings, wrong types, foreign coordinates and malformed protocol framesat the deployed server; a refusal with a usable message passes, a 500 or aconfident answer to a question it should not answer fails. It found three realbugs the happy-path suites had missed.
Checking it without trusting this repository
npm run prove exists because my own tests passing proves very little tosomeone who did not write them. It connects with the official MCP client SDK,then takes every number the server reported and re-fetches the same day straightfrom Open-Meteo, comparing field by field, and prints the upstream URL it usedso you can open it yourself.
Three more ways, needing nothing from here:
# Anthropic's own inspector, not my code
npx @modelcontextprotocol/inspector --cli https://rain-check-mu.vercel.app/mcp --transport http --method tools/list
# raw JSON-RPC, no client, no session, because it is stateless
curl -s -X POST https://rain-check-mu.vercel.app/mcp -H 'Content-Type: application/json' -H 'Accept: application/json, text/event-stream' -d '{"jsonrpc":"2.0","id":1,"method":"tools/list"}'
# let your own client run its health check against it
claude mcp add --transport http rain-check https://rain-check-mu.vercel.app/mcp
claude mcp list
And the version that needs only a browser: open both of these and compare thedates. rain_mm in the first equals precipitation_sum in the second.
- https://rain-check-mu.vercel.app/v1/workability?location=Bendigo&trade=concreting&days=3
- https://api.open-meteo.com/v1/forecast?latitude=-36.75818&longitude=144.28024&daily=precipitation_sum&timezone=Australia/Melbourne
Deploy
vercel deploy --prod
How it is laid out
src/core.ts the six operations, with no transport in them
src/mcpServer.ts the MCP tool surface
src/lib/ http, dates, geocoding, forecast, holidays, thresholds, verdicts
api/mcp.ts Streamable HTTP, stateless
api/v1/[op].ts the same operations over REST
api/openapi.ts the OpenAPI document, generated from the same constants
api/health.ts calls every upstream and reports real latency
public/index.html the landing page, including the build log
scripts/ the three verification runs
Both front doors import src/core.ts. That is the only way the custom GPT andthe MCP client can be trusted to give the same answer, and it means a thresholdfixed once is fixed everywhere.
What it will not do
- Present a threshold as a safety clearance. They are planning defaults, shownin every answer and overridable per call.
- Guess past the sixteen-day forecast. Later dates come back in
out_of_rangewith the reason and no data. - Let third-party holiday data pass as authoritative. It is state level only,carries no regional or show days, and every response links the official stategovernment page.
- Fill a gap with a guess. When an upstream is unreachable the tool says whichone and what to do, and tells the model not to substitute an opinion.
- Pick between two Richmonds. Ambiguity comes back as candidates.
Data sources
- Weather and geocoding: Open-Meteo, CC BY 4.0.
- Public holidays: Nager.Date, third party, state levelonly.
The Bureau of Meteorology's API is not used: its own terms say "You must notuse, copy or share it".
