Open Ephemeris — Claude Code MCP server: what it does, how to install
Supplies sub-arcsecond planetary positions and chart calculations from NASA JPL DE440 ephemeris data. Eliminates hallucinated degrees in AI outputs.
claude mcp add --transport http open-ephemeris https://mcp.openephemeris.com/mcpWhat Open Ephemeris does
The server connects language models to a calculation engine built on NASA JPL DE440 files. It covers 1,100 years of astronomical movements across 90 celestial bodies and 124 fixed stars. Instead of guessing zodiac degrees, the model calls tools like ephemeris_natal_chart to pull verified numbers.
You can reach it through the hosted endpoint at https://mcp.openephemeris.com/mcp using Streamable HTTP, or run @openephemeris/mcp-server locally via npx. Creating a free account provides 150 request credits.
Every timestamp parameter requires an explicit timezone string or UTC offset. Passing a bare clock time without zone metadata causes calculation failures.
What it helps with
- compute natal charts with exact birth coordinates and timezones
- fetch verified planetary degrees without model hallucinations
- track positions of asteroids and fixed stars across historical dates
- connect NASA astronomical ephemeris tools to coding agents
Example prompts for the agent
- Look up the exact positions of planets and fixed stars for 2000-01-01T00:00:00Z.
- Run transit calculations against birth coordinates at latitude 41.8781 and longitude -87.6298.
How to install Open Ephemeris
Platform CLI: remote server
claude mcp add --transport http open-ephemeris https://mcp.openephemeris.com/mcpPlatform CLI: remote server
codex mcp add open-ephemeris --url https://mcp.openephemeris.com/mcpConfig file
{
"mcpServers": {
"open-ephemeris": {
"url": "https://mcp.openephemeris.com/mcp"
}
}
}Config file
{
"servers": {
"open-ephemeris": {
"type": "http",
"url": "https://mcp.openephemeris.com/mcp"
}
}
}Platform CLI: remote server
gemini mcp add -t http open-ephemeris https://mcp.openephemeris.com/mcpStep by step, with commands for each platform: How to add an MCP server to Claude Code, Codex, Cursor, VS Code, Gemini CLI and more
Questions about Open Ephemeris
How do I install Open Ephemeris in Claude Code?
Run claude mcp add --transport http open-ephemeris https://mcp.openephemeris.com/mcp. This attaches the hosted HTTP endpoint directly to your agent.
What does Open Ephemeris do?
It supplies tools for calculating astrological charts and planetary positions. All output comes directly from NASA JPL DE440 ephemeris data.
Do I need an API key to run it?
Direct SDK and npx setups require a key from openephemeris.com/dashboard. A free account includes 150 starter credits.
