table-mountain-mcp

An MCP server that lets an agent answer "should I go up Table Mountain today?" and "which day this week is best?" using tablemountainweather.com, which I built.

It ships with an eval suite, because a tool description is the agent's only documentation and the only way to know whether it works is to watch agents use it.

Tools

Both are read-only and call one public endpoint, GET https://tablemountainweather.com/api/verdict, cached for five minutes (the site refreshes every ten).

Related MCP server: bergauf

Design decisions

• Freshness is part of the answer. Every result has a freshness block: when the data was observed, its age, the Cape Town date it was made for, and stale: true with a plain-language note if it's old or from another day. While building this, the live endpoint served a verdict observed the previous day. An agent reading "verdict: no" without that context would give the wrong advice with full confidence.

• "Today" means today in Cape Town, not on the agent's server. Cape Town is UTC+2, so at 23:30 UTC it is already tomorrow there. There's a test for that.

• Say what's missing instead of dropping it. Dates past the 7-day forecast come back in notInForecast, so the agent says "no forecast yet" rather than silently answering about other days.

• Errors tell the agent what to do. When the site is down the tool returns an error that says not to estimate the weather and where the user can check.

• Weather and the cable car are separate questions. A good-weather day while the cableway is closed for maintenance gets a cablewayNote.

• Defensive parsing. The response is validated with Zod and unknown fields pass through, so a site change produces a clear error rather than wrong numbers.

Install

Requires Node 20+.

git clone https://github.com/cobus-meyer/table-mountain-mcp && cd table-mountain-mcp
npm install && npm run build

Claude Code:

claude mcp add table-mountain -- node /absolute/path/to/table-mountain-mcp/dist/index.js

Claude Desktop, Cursor or any stdio MCP client:

{
  "mcpServers": {
    "table-mountain": { "command": "node", "args": ["/absolute/path/to/table-mountain-mcp/dist/index.js"] }
  }
}

Tests

npm test

Tests drive the server through a real MCP client over an in-memory transport: ranking, stale data, the Cape Town midnight edge, out-of-range dates, a closed cableway, a site outage, bad input, caching and a changed response shape.

Evals

evals/cases.ts holds 12 questions a real user would ask, each run against a frozen API response and a frozen clock:

Each case starts a fresh agent with the server attached and grades the transcript: were the right tools called, does the answer contain the facts that matter, and does it avoid the mistakes that matter. Grading is rule-based on purpose so it's cheap, repeatable and easy to dispute.

npm run eval:check                                   # offline: cases, fixtures and tools are valid
ANTHROPIC_API_KEY=... npm run eval                   # run all cases once
npm run eval -- --runs 3 --model claude-haiku-5-5    # repeat to see variance
npm run eval -- --descriptions baseline              # compare one-line tool descriptions

--descriptions baseline swaps in the one-line tool descriptions most servers ship, so the effect of writing descriptions for agents can be measured instead of assumed. Results are written to evals/results/.

Results

12 cases, 3 runs each, on claude-haiku-5-5, run on 2026-11-03.

The only failure was last-car on baseline, in all 3 runs: the agent said it had no access to the cable car schedule and never called a tool, because the one-line description only mentions a weather verdict. v1 names cable car status and hours in its description and passed all 3 runs. With no v1 failures, nothing changed after these runs.

Fixtures

fixtures/windy-monday.json is a real response from the live API. calm-monday.json and cableway-closed.json are edited copies of it for cases the live API wasn't showing at the time.

License

MIT