VÆR

An opinionated Model Context Protocol (MCP) server that provides high-level, LLM-friendly weather tools backed by MET Norway’s Weather API (api.met.no), via an internal metno-proxy (Nginx reverse proxy + cache).

This server is designed to be used by MCP-compatible clients (e.g. AI assistants, IDEs, custom apps) to get structured weather information and simple “weather services” like activity planning and marine trip risk assessments.

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Example Usage from a MCP Client

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Getting Started

# Clone the repository
git clone [email protected]:bitjungle/vaer.git
# git clone https://github.com/bitjungle/vaer.git
cd vaer

# Start the stack (requires Docker)
make compose-build && make up

# Verify it's running
curl http://localhost:8080/healthz   # → ok
curl http://localhost:3000/health    # → {"status":"ok","transport":"http"}

That's it — you now have a running MCP server. See Documentation for next steps.

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Features

• Opinionated weather tools

  • weather_get_location_forecast – normalized hourly forecast
  • weather_get_nowcast – short-term precipitation and conditions
  • weather_get_air_quality – air quality & AQI for Norwegian locations
  • weather_get_recent_observations – recent observed weather (Frost)
  • weather_get_marine_conditions – coastal/marine summary
  • weather_assess_outdoor_activity_window – "when is it nice outside?"
  • weather_assess_marine_trip_risk – simple marine risk evaluation

• Norwegian place name resolution (28,115 places)

  • places_resolve_name – resolve Norwegian place names to coordinates
  • Powered by Kartverket Stedsnavn (official Norwegian place names register)
  • Supports queries like "What's the weather in Bergen?"
  • Intelligent matching with FTS5 full-text search, confidence scoring and disambiguation
  • Local SQLite database (6.09 MB), ~5ms query latency

• MCP-native

  • Exposes tools, resources, and prompts using the MCP specification.
  • Supports stdio and HTTP transports.

• Backed by metno-proxy

  • Uses your existing Nginx proxy for:
    • Proper User-Agent handling (required by MET Norway)
    • Caching and rate limiting
    • Health checks

• Structured, consistent outputs

  • Normalized units (°C, m/s, mm/h, etc.)
  • Structured JSON-like responses + short textual summaries
  • Includes metadata about data source, licensing and cache freshness

• Attribution & compliance

  • Built-in resources for MET Norway license & credit lines.
  • Designed to respect MET usage guidelines.

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Architecture

High-level architecture:

MCP Client (ChatGPT, IDE, custom app)
        │  (MCP / JSON-RPC)
        ▼
   Vær Server
        ├─ Weather Domain (MET-backed)
        │    │  (HTTP, internal)
        │    ▼
        │  metno-proxy (Nginx: cache, UA, rate limit)
        │    │  (HTTPS)
        │    ▼
        │  api.met.no (MET Norway Weather API)
        │
        └─ Places Domain (Norway gazetteer)
             │  (local SQLite query)
             ▼
           data/places.db (Stedsnavn-derived)

• The MCP server never calls api.met.no directly.
• All upstream traffic goes through metno-proxy.
• Place name resolution uses a local SQLite database (no network calls).

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Requirements

• Runtime

  • Node.js 24+ (LTS or newer)

• MET proxy

  • A running metno-proxy container or service that:

    • Proxies /weatherapi/... to https://api.met.no/...
    • Sets a compliant User-Agent
    • Optionally enables caching & rate limiting

• Docker + Compose v2 (for Docker deployments)

  • macOS/Windows: Install Docker Desktop (includes everything)
  • Linux servers: Install Docker CE from Docker's official repository — see docs/docker-linux.md

• Places Database (included)

  • data/places.db (28,115 Norwegian places, 6.09 MB) is included in the repository
  • No setup required — works out of the box after git clone
  • Developers can regenerate from source — see docs/etl-pipeline.md

• MCP Client

  • Any client that supports MCP servers over stdio or HTTP.

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Configuration

The MCP server is configured via environment variables:

Required

• METNO_PROXY_BASE_URL Base URL to the Nginx proxy (e.g. http://localhost:8080 for dev, http://metno-proxy:80 for Docker).

Proxy & Timeouts

• METNO_TIMEOUT_MS — Upstream HTTP timeout (default: 5000ms)
• METNO_CONNECT_TIMEOUT_MS — Connection timeout (default: 2000ms)

Frost API (Observations)

• FROST_CLIENT_ID — Client ID for Frost API (get from https://frost.met.no/auth/requestCredentials.html)
• FROST_BASE_URL — Override Frost API base URL (default: https://frost.met.no)
• FROST_TIMEOUT_MS — Frost API timeout (default: 10000ms)

Server

• VAER_PORT — Port for HTTP transport. If not set, server uses stdio transport.
• VAER_LOG_LEVEL — Logging level: debug, info, warn, error (default: info)

Authentication

• VAER_AUTH_MODE — Authentication mode: none, api-key, jwt (default: none)
• VAER_API_KEY — API key value (required if VAER_AUTH_MODE=api-key)

Places Database

• PLACES_DB_PATH — Path to SQLite places database (default: ./data/places.db)

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Usage

1. Run metno-proxy Start the Nginx-based proxy that fronts api.met.no.

2. Run the Vær server Start the MCP server process (via node, npm, pnpm, or Docker), pointing it at METNO_PROXY_BASE_URL.

3. Connect from an MCP client Configure your MCP-compatible client to connect to this server:

   • via stdio (local)
   • or via HTTP (remote), using the configured port and optional API key.

4. Call tools from the client The client can now call any of the 7 implemented tools:

   Data Tools:

   • weather_get_location_forecast – Global weather forecasts
   • weather_get_nowcast – Nordic 2-hour precipitation
   • weather_get_air_quality – Norway air quality & AQI
   • weather_get_marine_conditions – Coastal marine weather
   • weather_get_recent_observations – Observed weather (Frost API)

   Service Tools:

   • weather_assess_outdoor_activity_window – Activity planning with comfort scoring
   • weather_assess_marine_trip_risk – Marine trip risk assessment

   Places Tool:

   • places_resolve_name – Resolve Norwegian place names to coordinates

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Repository Layout

.
├─ src/                       # TypeScript source code
│  ├─ index.ts               # MCP server entry point
│  ├─ tools/                 # 8 MCP tools (weather_* + places_*)
│  ├─ resources/             # MCP resources
│  ├─ prompts/               # MCP prompts
│  ├─ domain/                # Shared utilities
│  └─ places/                # Places module
├─ data/
│  └─ places.db              # Norwegian places database (included)
├─ docs/                      # Documentation
│  ├─ getting-started.md     # Deployment guide
│  ├─ development.md         # Developer setup
│  ├─ design.md              # Architecture & API specs
│  └─ ...                    # See docs/README.md
├─ metno-proxy/               # Nginx reverse proxy
├─ scripts/etl/               # Places ETL (developer-only)
├─ tests/                     # Test suites
├─ docker-compose.yml         # Full stack orchestration
└─ Makefile                   # Build commands

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Quick Start (Development)

Prerequisites

• Node.js 24+ LTS
• Docker Desktop (macOS/Windows) or Docker + Compose v2 (Linux — see Requirements)

Running the Full Stack

# Build and start all services
make compose-build
make up

# Verify services are running
docker compose ps

# Test endpoints
curl http://localhost:8080/healthz
curl http://localhost:3000/health

Both services should show as "healthy":

• metno-proxy: http://localhost:8080 (nginx proxy to api.met.no)
• vaer: http://localhost:3000 (MCP server with HTTP transport)

For detailed setup instructions, see docs/development.md.

Testing

# Run all tests
npm test

# Unit tests only
npm run test:unit

# Integration tests (requires metno-proxy running)
METNO_PROXY_BASE_URL=http://localhost:8080 npm run test:integration

# Test with MCP Inspector
npm run build
METNO_PROXY_BASE_URL=http://localhost:8080 npx @modelcontextprotocol/inspector node dist/index.js

For detailed testing instructions, see docs/development.md.

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Deployment

The Vær server can be deployed in multiple ways:

Docker Compose (Recommended)

Deploy the full stack (metno-proxy + vaer) with a single command:

# 1. Build and start all services
make compose-build
make up

# 2. Verify deployment
docker compose ps
curl http://localhost:8080/healthz

# 3. View logs
make compose-logs

# 4. Stop services
make down

Environment Configuration:

Create a .env file in the project root:

# Required: Your User-Agent for MET Norway API
METNO_USER_AGENT=my-service/1.0 [email protected]

# Optional: Frost API credentials for observations
FROST_CLIENT_ID=your-frost-client-id

# Optional: Logging level
VAER_LOG_LEVEL=info

Standalone Docker

Build and run the MCP server image directly:

# Build image
docker build -t vaer:latest .

# Run with environment variables
docker run -d \
  --name vaer \
  -e METNO_PROXY_BASE_URL=http://metno-proxy:80 \
  -e VAER_LOG_LEVEL=info \
  vaer:latest

Note: The places.db database is baked into the image during build. Do not mount ./data as a volume — it causes permission issues.

MCP Client Configuration

Connect MCP clients (Claude Desktop, VS Code, etc.) to the server:

Claude Desktop (~/Library/Application Support/Claude/claude_desktop_config.json):

{
  "mcpServers": {
    "vaer": {
      "command": "node",
      "args": ["/path/to/vaer/dist/index.js"],
      "env": {
        "METNO_PROXY_BASE_URL": "http://localhost:8080"
      }
    }
  }
}

Docker-based setup:

{
  "mcpServers": {
    "vaer": {
      "command": "docker",
      "args": [
        "run", "--rm", "-i",
        "--network", "vaer_vaer-network",
        "-e", "METNO_PROXY_BASE_URL=http://metno-proxy:80",
        "vaer:latest"
      ]
    }
  }
}

See examples/client-configs/ for more configuration examples.

Production Deployment

For production deployments, see docs/getting-started.md:

• Docker Compose production configuration
• Kubernetes manifests
• Security considerations
• Monitoring & operations

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Documentation

Guide	Description
Getting Started	Production deployment guide
Development	Local setup, testing, contributing
Design	Architecture, API schemas, tool specifications
Docker on Linux	Installing Docker CE on Ubuntu/Debian
Metno Proxy	Nginx proxy configuration
Observability	Metrics, logging, debugging
ETL Pipeline	Regenerating places.db (developer-only)
History	Implementation history
Roadmap	Future plans

See docs/README.md for the complete documentation index.

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License

VÆR is open-source software licensed under the MIT License. However, the author respectfully requests that it not be used for military, warfare, or surveillance applications.