Caelus MCP

Astrology/ephemeris MCP server: 9 chart tools — positions, houses, aspects, transits, electional.

Quick Install

Automated & IDE Setup

Copy the AI prompt to install this server into Claude Code, Cursor, or another agent — or use 1-click editor setup below.

Add to Cursor Add to VS Code

Manual Client & Custom JSON ConfigExpand JSON ▾

Client Config & Setup

Choose your client or environment

Target File:~/Library/Application Support/Claude/claude_desktop_config.json

claude_desktop_config.json

{
  "mcpServers": {
    "caelus-mcp": {
      "command": "npx",
      "args": [
        "-y",
        "caelus-mcp"
      ]
    }
  }
}

💡 Paste the JSON block into your client's configuration file under mcpServers, then restart the application.

Documentation Overview

Caelus

Clean-room astrology computation monorepo. MIT, no Swiss Ephemeris code, no AGPL, no ephemeris files. Caelus computes ephemeris positions, charts, events, hellenistic timing techniques, Vedic methods, citable chart facts, sky-view image-prompt frames, and the MCP tools around them. Live at ephemengine.com.

Packages

Path	npm	Description
`packages/caelus`	`caelus`	TypeScript engine (~153 KB gzipped total, zero deps)
`packages/caelus-mcp`	`caelus-mcp`	MCP server: charts, transits, synastry, events, eclipses
`packages/caelus-delineations-pd`	—	Public-domain interpretation corpus + default validation set for `interpret()`
`packages/birth`	`caelus-birth`	Birth time + place → UT (timezone and DST resolution)
`packages/wheel`	`caelus-wheel`	React SVG chart wheel, zero runtime deps
`apps/web`	—	Next.js site: playground, validation, edge `/api/chart`
`caelus-starter`	—	Next.js starter app (separate repo)

The Python reference engine and data-fitting pipeline live in python/; they mint the coefficient data and golden fixtures and are not a runtime dependency.

Docs

ARCHITECTURE.md — layout, durability decisions, product strategy
MCP_SPEC.md — MCP tool contract
docs/gap-analysis.md — Swiss Ephemeris comparison (closed at 0.5.0)
docs/agents.md — pitfalls for coding agents building on Caelus
docs/releasing.md — release process

Quick start

Terminal

npm install
npm run build
npm test
npm run dev -w web

http://localhost:3000 — live chart in the browser. Edge API: GET /api/chart?date=…&lat=…&lon=….

Branches

main — stable releases
dev — active development

Read the full README →View source on GitHub →

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Frequently Asked Questions about Caelus MCP

Add the following block to your claude_desktop_config.json under mcpServers: "mcpServers": { "caelus-mcp": { "command": "npx", "args": ["-y", "caelus-mcp"] } }

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Technical Specs & Signals

CategoryDeveloper Tools

27Quality signal: Emerging · 27/100How this signal is calculated ▾

Server availabilityNot measured

Not scored for repo-hosted servers — we can't reach the running server, only its GitHub page. Hosted MCP endpoints are health-checked live.

Verified ownership8/20

Documentation & tools11/30

Adoption & activity1/15

Community engagement0/10

A guidance signal from public completeness & health data — not a user rating. New listings start lower and rise as they add docs, get verified, and grow adoption. Signals we can't observe for a listing are skipped, not counted against it.

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