OpenEphemeris MCP Server

Model Context Protocol server for OpenEphemeris — 52 typed astrology tools powered by the NASA JPL DE440 ephemeris. Zero hallucination on planetary positions, dates, and degrees. Covers 1,100 years of astronomical data.

Hosted endpoint: https://mcp.openephemeris.com/mcp (Streamable HTTP, MCP 2025-11-25 spec)

Quick Start

Install via Smithery (recommended)

The fastest way to connect any MCP-compatible client:

npx -y @smithery/cli install @open-ephemeris/openephemeris --client claude

Or browse the listing and copy connection snippets: smithery.ai/servers/open-ephemeris/openephemeris

---

Connect via AI SDK (Vercel AI SDK)

import Smithery from "@smithery/api"
import { createMCPClient } from "@ai-sdk/mcp"
import { generateText } from "ai"
import { anthropic } from "@ai-sdk/anthropic"
import { createConnection } from "@smithery/api/mcp"

const smithery = new Smithery()

const conn = await smithery.connections.create("{your-namespace}", {
  mcpUrl: "https://server.smithery.ai/open-ephemeris/openephemeris",
  headers: {
    apiKey: "your-openephemeris-api-key", // get one free at openephemeris.com/dashboard
  },
})

const { transport } = await createConnection({
  client: smithery,
  namespace: "{your-namespace}",
  connectionId: conn.connectionId,
})

const mcpClient = await createMCPClient({ transport })
const tools = await mcpClient.tools()

const { text } = await generateText({
  model: anthropic("claude-sonnet-4-20250514"),
  tools,
  prompt: "Calculate a natal chart for someone born April 15, 1990 at 2:30 PM in Chicago.",
})

await mcpClient.close()

Connect via MCP SDK (TypeScript)

import Smithery from "@smithery/api"
import { Client } from "@modelcontextprotocol/sdk/client/index.js"
import { createConnection } from "@smithery/api/mcp"

const smithery = new Smithery()

const conn = await smithery.connections.create("{your-namespace}", {
  mcpUrl: "https://server.smithery.ai/open-ephemeris/openephemeris",
  headers: {
    apiKey: "your-openephemeris-api-key",
  },
})

const { transport } = await createConnection({
  client: smithery,
  namespace: "{your-namespace}",
  connectionId: conn.connectionId,
})

const mcpClient = new Client(
  { name: "my-app", version: "1.0.0" },
  { capabilities: {} }
)
await mcpClient.connect(transport)

const { tools } = await mcpClient.listTools()
const result = await mcpClient.callTool({
  name: "ephemeris_natal_chart",
  arguments: { datetime: "1990-04-15T14:30:00", latitude: 41.8781, longitude: -87.6298, format: "llm" },
})

Connect directly (Streamable HTTP, no Smithery)

import { StreamableHTTPClientTransport } from "@modelcontextprotocol/sdk/client/streamableHttp.js"
import { Client } from "@modelcontextprotocol/sdk/client/index.js"

const transport = new StreamableHTTPClientTransport(
  new URL("https://mcp.openephemeris.com/mcp"),
  { requestInit: { headers: { "X-API-Key": "your-openephemeris-api-key" } } }
)

const client = new Client({ name: "my-app", version: "1.0.0" }, { capabilities: {} })
await client.connect(transport)

---

One-click install (Cursor)

<!-- GENERATED:CURSOR_INSTALL:BEGIN -->

Replace YOUR_API_KEY_HERE in Cursor MCP settings with your API key from https://openephemeris.com/dashboard.

Cursor deeplink payload:

{
  "command": "npx",
  "args": [
    "-y",
    "@openephemeris/mcp-server"
  ],
  "env": {
    "OPENEPHEMERIS_PROFILE": "dev",
    "OPENEPHEMERIS_BACKEND_URL": "https://api.openephemeris.com",
    "OPENEPHEMERIS_API_KEY": "YOUR_API_KEY_HERE"
  }
}

<!-- GENERATED:CURSOR_INSTALL:END -->

Manual install (stdio MCP clients)

{
  "mcpServers": {
    "openephemeris": {
      "command": "npx",
      "args": ["-y", "@openephemeris/mcp-server"],
      "env": {
        "OPENEPHEMERIS_PROFILE": "dev",
        "OPENEPHEMERIS_BACKEND_URL": "https://api.openephemeris.com",
        "OPENEPHEMERIS_API_KEY": "YOUR_API_KEY_HERE"
      }
    }
  }
}

Platform guide

Detailed setup walkthroughs for each platform are in SETUP.md.

Client	Install mode	Config location
Smithery	One-click	smithery.ai
Cursor	One-click deeplink or manual	~/.cursor/mcp.json
Claude Desktop (macOS)	Manual	~/Library/Application Support/Claude/claude_desktop_config.json
Claude Desktop (Windows)	Manual	%APPDATA%\Claude\claude_desktop_config.json
Windsurf	Manual	~/.codeium/windsurf/mcp_config.json (or legacy ~/.codeium/mcp_config.json)
Claude Web / ChatGPT / remote clients	Hosted URL	https://mcp.openephemeris.com/mcp

Client install walkthroughs

1. Cursor
   • Click the "Install in Cursor" button above, then replace YOUR_API_KEY_HERE in Cursor MCP settings.
   • If you prefer manual setup, paste the mcpServers.openephemeris block from "Manual install" into ~/.cursor/mcp.json.
2. Claude Desktop (macOS/Windows)
   • Open the platform config file from the table above.
   • Add the same mcpServers.openephemeris block from "Manual install".
   • Restart Claude Desktop.
3. Windsurf
   • Open ~/.codeium/windsurf/mcp_config.json (or the legacy ~/.codeium/mcp_config.json path).
   • Add the mcpServers.openephemeris block from "Manual install".
   • Restart Windsurf.

Remote-only clients (Claude Web, ChatGPT, etc.)

The server is hosted at https://mcp.openephemeris.com/mcp with full Streamable HTTP support (MCP 2025-11-25 spec). Remote-only clients can connect directly — no bridge/proxy required:

• Claude Web: Add https://mcp.openephemeris.com/mcp as a remote MCP server with X-API-Key: your-key header
• Via Smithery: Use the Smithery listing for managed connections with any client
• Legacy SSE: https://mcp.openephemeris.com/sse remains available for SSE-only clients

Auth and upgrade behavior in MCP clients

• Missing/invalid credentials (401): tool call fails with a message that points users to sign up/sign in at https://openephemeris.com/login?signup=true&redirect=%2Fdashboard%3Ftab%3Daccount, then create/manage keys in https://openephemeris.com/dashboard?tab=account.
• Tier-gated endpoint (403): tool call returns an upgrade-required message with https://openephemeris.com/pay and dashboard billing/key management link.
• Monthly quota exhausted (402): tool call returns usage quota guidance with both dashboard (/dashboard?tab=account) and upgrade (/pay) links.
• Burst/rate limit (429): tool call returns retry guidance and links to dashboard usage monitoring.

What You Can Ask

"Calculate a natal chart for 1990-04-15 at 2:30 PM in Chicago."
"Find all Saturn transits to my natal Sun in the next 6 months."
"Get the current moon phase and void-of-course status."
"Find the next solar eclipse visible from Tokyo."
"Find the best time to sign a contract in March — electional window."
"Generate a Human Design chart for my birth data."
"What is my Vedic (sidereal) chart?"
"Calculate my Chinese BaZi (Four Pillars) chart."
"Show me my Astrocartography power lines — where is my Venus line on the map?"
"Find all ACG lines within 3° of Paris for my chart."
"Calculate a synastry chart between two people."
"Find the next Venus Star Point and my relationship to it."
"What are the active planetary stations in the next 3 months?"
"Calculate primary directions for the next 5 years."
"Find my Firdaria time lord period."
"What is the sidereal time and delta-T right now?"

Tools at a Glance

Category	Tool	Tier
Natal chart	ephemeris_natal_chart	Explorer
Transit forecast	ephemeris_transits	Explorer
Transit chart snapshot	ephemeris_natal_transits	Explorer
Moon phase / VOC	ephemeris_moon_phase	Explorer
Eclipse next visible	ephemeris_next_eclipse	Explorer
Electional window	ephemeris_electional	Developer
Moment analysis	electional_moment_analysis	Developer
Station tracker	electional_station_tracker	Developer
Aspect search	electional_aspect_search	Developer
Human Design chart	human_design_chart	Explorer
HD composite	human_design_composite	Explorer
HD penta	human_design_penta	Explorer
HD return / opposition	hd_planetary_return, hd_opposition	Explorer
Vedic chart	vedic_chart	Explorer
BaZi (Chinese)	chinese_bazi	Explorer
Synastry	ephemeris_synastry	Developer
Composite chart	ephemeris_composite	Developer
Relocation chart	ephemeris_relocation	Developer
Progressed chart	ephemeris_progressed_chart	Explorer
Solar return	ephemeris_solar_return	Developer
Lunar return	ephemeris_lunar_return	Developer
Planetary return	ephemeris_planetary_return	Developer
Astrocartography lines	acg_power_lines	Developer
ACG hits at location	acg_hits	Scale
Venus Star Points	venus_star_points + 4 more	Explorer
Chart wheel image	ephemeris_chart_wheel	Developer
Bi-wheel image	ephemeris_bi_wheel	Developer
Dignities / Midpoints / Fixed stars	ephemeris_dignities, ephemeris_midpoints, ephemeris_fixed_stars	Explorer

Tooling Model

• Typed tools are preferred for common workflows (natal, transits, moon phase, eclipse, synastry, relocation, electional, Human Design).
• Generic tools: dev.list_allowed returns all currently allowlisted operations, and dev.call invokes any allowlisted operation by method + path.
• Security model: default-deny with explicit allowlist in config/dev-allowlist.json.
• Deny prefixes block sensitive route families (/auth, /billing, /admin, etc.).

dev.call input

Parameter	Type	Required	Description
method	GET|POST|PUT|PATCH|DELETE	Yes	HTTP method
path	string	Yes	Absolute API path, e.g. /ephemeris/natal-chart
query	object	No	Query parameters
body	object	No	JSON body for non-GET requests
preset	full|simple	No	Convenience mapping to query.preset
format	json|llm|llm_v2	No	Convenience mapping to query.format (llm_v2 normalizes to llm)
output_mode	full|simple|llm|llm_v2	No	Legacy compatibility field

Environment Variables

Variable	Required	Description
OPENEPHEMERIS_API_KEY	Yes (unless service key/JWT used)	API key for OpenEphemeris
ASTROMCP_API_KEY	No	Legacy alias for OPENEPHEMERIS_API_KEY (checked as fallback)
OPENEPHEMERIS_BACKEND_URL	No	Defaults to https://api.openephemeris.com
OPENEPHEMERIS_PROFILE	No	dev by default
OPENEPHEMERIS_SERVICE_KEY	No	Internal service auth
OPENEPHEMERIS_JWT	No	Bearer token auth
OPENEPHEMERIS_DEV_ALLOWLIST_PATH	No	Override allowlist file path
MCP_USER_ID	No	Per-instance user identifier

Legacy aliases (ASTROMCP_*, MERIDIAN_*) remain supported.

Legal

This package is licensed under the MIT License. However, use of this package to access the OpenEphemeris API constitutes use of the Service and is governed by the OpenEphemeris Terms of Service. By using this package, you agree to those terms. See also the Privacy Policy and Acceptable Use Policy.

Development

npm install
npm run dev
npm run typecheck
npm test
npm run regen:dev-allowlist
npm run check:dev-allowlist
npm run sync:readme
npm run check:readme
npm run verify:release

Deploying the SSE Server to Fly.io

When you update the MCP server logic (handlers, bug fixes, hardening), you should deploy it so clients connecting via the remote https://mcp.openephemeris.com/mcp endpoint get the updates immediately.

1. Navigate to apps/api/mcp-server
2. Run fly deploy --remote-only

Note on NPM: Deploying to Fly.io instantly updates the web-accessible SSE tool. However, users installing your tool locally in Cursor/Desktop via npx @openephemeris/mcp-server will only receive the updates once a new version is published to NPM. If your changes are critical, you should bump the version in package.json and run npm publish (or your CI release pipeline) after deploying to Fly.

npm run verify:release is the release gate. It checks:

• allowlist freshness against OpenAPI
• schema pack freshness
• README synchronization
• type safety + tests
• publish tarball contents (npm pack --dry-run --json)

Architecture

┌─────────────────────────────────────────────────────────┐
│                    MCP Clients                          │
│  Smithery Gateway · Claude Web · ChatGPT · Remote apps  │
└──────────────────┬──────────────────────────────────────┘
                   │ Streamable HTTP (MCP 2025-11-25)
                   │ https://mcp.openephemeris.com/mcp
                   │
┌─────────────────────────────────────────────────────────┐
│          Cursor · Claude Desktop · Windsurf             │
└──────────────────┬──────────────────────────────────────┘
                   │ stdio JSON-RPC
                   │ npx @openephemeris/mcp-server
                   │
              ┌────▼────────────────────┐
              │  openephemeris-mcp      │
              │  Node.js MCP Server     │
              │  52 typed tools         │
              │  auth: Key > JWT        │
              └────────────┬────────────┘
                           │ HTTPS
                           ▼
              ┌────────────────────────┐
              │  OpenEphemeris API     │
              │  api.openephemeris.com │
              │  NASA JPL DE440        │
              │  1,100 years of data   │
              └────────────────────────┘

<!-- GENERATED:RUNTIME_SNAPSHOT:BEGIN -->

Runtime Snapshot (Generated)

Generated by npm run sync:readme from config/dev-allowlist.json and the live tool registry.

• Allowlisted operations: 23
• Methods: GET=4, POST=19, PUT=0, PATCH=0, DELETE=0
• Registered tools (OPENEPHEMERIS_PROFILE=dev): 52
• Typed tools: acg_hits, acg_power_lines, auth_login, auth_logout, auth_status, chinese_bazi, dev_call, dev_list_allowed, electional_aspect_search, electional_moment_analysis, electional_station_tracker, ephemeris_angles_points, ephemeris_aspect_check, ephemeris_bi_wheel, ephemeris_chart_wheel, ephemeris_composite, ephemeris_composite_midpoint, ephemeris_dignities, ephemeris_electional, ephemeris_fixed_stars, ephemeris_hermetic_lots, ephemeris_house_cusps, ephemeris_lunar_return, ephemeris_midpoints, ephemeris_moon_phase, ephemeris_natal_batch, ephemeris_natal_chart, ephemeris_natal_transits, ephemeris_next_eclipse, ephemeris_next_lunar_phase, ephemeris_overlay, ephemeris_planet_position, ephemeris_planetary_return, ephemeris_progressed_chart, ephemeris_relocation, ephemeris_retrograde_status, ephemeris_solar_return, ephemeris_synastry, ephemeris_transits, hd_opposition, hd_planetary_return, human_design_bodygraph, human_design_chart, human_design_composite, human_design_penta, vedic_chart, venus_eight_year_star, venus_elongations, venus_phase, venus_star_points, venus_star_points_conjunctions, venus_stations
• Generic tools:

Allowlist Families

Family	Operations	Example
acg	4	POST /acg/ccg, POST /acg/hits
comparative	5	POST /comparative/composite, POST /comparative/composite/midpoint
electional	4	GET /electional/aspect-search, GET /electional/find-window
ephemeris	1	POST /ephemeris/relocation
predictive	6	POST /predictive/returns, POST /predictive/returns/lunar
visualization	3	POST /visualization/bi-wheel, POST /visualization/bodygraph
<!-- GENERATED:RUNTIME_SNAPSHOT:END -->

Why OpenEphemeris for AI Agents?

Most LLMs (like Claude and ChatGPT) struggle heavily with astronomical calculations (trigonometry, Julian date conversions, and planetary lookups). OpenEphemeris serves as a secure, remote math engine.

By pairing LLMs with the OpenEphemeris MCP server, your agents can instantly access:

• Zero-hallucination coordinates: Direct, sub-arcsecond NASA JPL DE440 calculations spanning 1,100 years of astronomical data.
• LLM-optimized tokens (format=llm): We compress standard 25,000 token JSON chart responses into minimal text blocks, cutting your inference costs by 50%.
• Ready-to-use astrology layers: Built-in support for Astrocartography geoJSON lines, Hermetic Lots, Fixed Stars, and complex Human Design matrix generation.