# Open Ephemeris

Supplies sub-arcsecond planetary positions and chart calculations from NASA JPL DE440 ephemeris data. Eliminates hallucinated degrees in AI outputs.

- MCP server · `type=mcp` · Claude Code, Codex, Cursor, GitHub Copilot, Windsurf (Devin Desktop), Cline, Zed, Gemini CLI · ★ 5
- Author: openephemeris
- License: MIT · policy=link-only · description only; the file stays with the author
- Source: https://github.com/openephemeris/openephemeris-MCP
- Updated: 2026-10-23
- HTML: https://affpapa.org/en/nevibecode/mcp/open-ephemeris

## What it 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.

## Requirements
- Remote server: `https://mcp.openephemeris.com/mcp`

## Install

### Claude Code (native platform)

**Platform CLI: remote server**
```bash
claude mcp add --transport http open-ephemeris https://mcp.openephemeris.com/mcp
```

### Codex

**Platform CLI: remote server**
```bash
codex mcp add open-ephemeris --url https://mcp.openephemeris.com/mcp
```

### Cursor

**Config file**
File `.cursor/mcp.json`:
```json
{
    "mcpServers": {
        "open-ephemeris": {
            "url": "https://mcp.openephemeris.com/mcp"
        }
    }
}
```

### GitHub Copilot

**Config file**
File `.vscode/mcp.json`:
```json
{
    "servers": {
        "open-ephemeris": {
            "type": "http",
            "url": "https://mcp.openephemeris.com/mcp"
        }
    }
}
```

### Gemini CLI

**Platform CLI: remote server**
```bash
gemini mcp add -t http open-ephemeris https://mcp.openephemeris.com/mcp
```

## When to use it
- 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
- 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.

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