SkyGazer MCP

A Model Context Protocol (MCP) server for planning a night of stargazing: is tonight good for it, what's visible, and what's happening in the sky worth going outside for. Built on NASA and JPL data (APOD, NeoWs, DONKI, JPL SSD, JPL Horizons, SVS), not just a wrapper around one API — the flagship tools cross-reference moon illumination, planet ephemeris, and geomagnetic activity into a plain-language answer instead of relaying a single endpoint's raw JSON.

There are other NASA MCP servers with broader endpoint coverage (Mars rover photos, EPIC Earth imagery, EONET, etc.) — this one trades that breadth for depth on one concrete use case: "is tonight worth going outside for?"

Status

Core tool set is built and wired into both Claude Code and Claude Desktop. See TODO.md for the live phase checklist and LEARNINGS.md for notes on MCP concepts and API quirks discovered along the way.

Tools

| Tool | What it does | API | | --- | --- | --- | | apod | Astronomy Picture of the Day — title, explanation, and the image itself | api.nasa.gov | | neows | Near-Earth objects in a date range (≤7 days), with hazard flags | api.nasa.gov | | geomagnetic_storms | Geomagnetic storms in a date range, with an aurora-visibility estimate for a given lat/lon | api.nasa.gov (DONKI) | | sbdb | Look up an asteroid/comet by name/designation — orbital elements + physical data | ssd-api.jpl.nasa.gov | | close_approach | Asteroids/comets passing close to Earth in a date range | ssd-api.jpl.nasa.gov | | sentry | Earth impact-risk assessment for a specific object | ssd-api.jpl.nasa.gov | | moon_phase | Moon phase/illumination for a date, with a stargazing-suitability note | svs.gsfc.nasa.gov | | stargazing_conditions | For a lat/lon + date: moon conditions plus which naked-eye planets are above the horizon | svs.gsfc.nasa.gov + ssd.jpl.nasa.gov (Horizons) |

Resources

| Resource | URI | What it is | | --- | --- | --- | | Mars Rovers | nasa://rovers | Static list of valid rover names + active date ranges |

Prerequisites

• Node.js (v24) and npm
• A free NASA API key from https://api.nasa.gov/ (or use DEMO_KEY for limited testing — 30 requests/hour, 50/day). Only needed for the api.nasa.gov-backed tools (apod, neows, geomagnetic_storms); the JPL/SVS-backed tools need no key at all.

Setup

npm install
cp .env.example .env   # then fill in your NASA_API_KEY
npm run build

Tech stack

• TypeScript
• @modelcontextprotocol/sdk (official MCP SDK for Node)
• Zod for tool input schema validation

Project structure

src/
  index.ts             # server entrypoint, transport wiring, tool/resource registration
  nasa-client.ts        # fetch wrapper for api.nasa.gov: injects api_key, normalizes errors
  ssd-client.ts          # fetch wrapper for ssd-api.jpl.nasa.gov (SBDB/CAD/Sentry): no key, serialized
  svs-client.ts           # fetch wrapper for svs.gsfc.nasa.gov (Dial-A-Moon): no key
  horizons-client.ts       # fetch wrapper for ssd.jpl.nasa.gov Horizons: no key, serialized, parses text ephemeris
  lib/moon.ts               # shared moon-phase-name / stargazing-note helpers
  resources/rovers.ts        # static Mars rovers resource
  tools/                      # one file per tool

Testing locally

Use the MCP Inspector to poke the server without needing a full client:

npm run inspect

Or run a quick scripted check with tsx + the MCP Client/StdioClientTransport classes — see past examples in this repo's history for the pattern.

Using it from Claude Code / Claude Desktop

Claude Code:

claude mcp add skygazer-mcp -- node --env-file=/absolute/path/to/MCP-NASA/.env /absolute/path/to/MCP-NASA/dist/index.js

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

{
  "mcpServers": {
    "skygazer-mcp": {
      "command": "node",
      "args": [
        "--env-file=/absolute/path/to/MCP-NASA/.env",
        "/absolute/path/to/MCP-NASA/dist/index.js"
      ]
    }
  }
}

Both require a full app/CLI restart to pick up a newly-registered server — MCP servers are loaded at startup, not hot-reloaded.