Caelus

MCP serverDev tools

Caelus is an astrology integration that gives your AI 34 tools for validated astrology work. Once added, your AI can generate charts, track planetary transits, read Vedic astrology, look up astrological facts, and view the sky.

Use Caelus in Claude, ChatGPT or Ahel Desktop

Free. Sign in, add Caelus and connect your AI. About a minute.

Claude ChatGPT Ahel Desktop

Also: Claude Code · Cursor · Codex

Then ask your AI: use the natal chart tool from Caelus

No key or account is asked for. Not verified by us yet: Ahel has not run a call through it.

Details

Available today. Use it from your connected AI after setup.

No key or account is asked for. Not verified by us yet: Ahel has not run a call through it.

After adding it, ask your AI to generate a chart or check the current transits to see what it can do.

CaelusStart free

What your AI can do with it

Generate astrology charts
Track planetary transits
Read Vedic astrology charts
Look up astrological facts
Show a view of the sky
Generate synthetic charts

Install Caelus

The server’s own address, for the clients that take one directly. Or connect Ahel once and every client you use reads it from one address, with the account kept on Ahel rather than in each client’s config.

Claude Code
claude mcp add --transport http --scope user caelus 'https://www.ephemengine.com/api/mcp'
Run it once in your project, then open /mcp to approve any sign-in the server asks for.
Claude Desktop
https://www.ephemengine.com/api/mcp
Add a custom connector in Settings, paste this address, and approve the sign-in.
Cursor
cursor://anysphere.cursor-deeplink/mcp/install?name=caelus&config=eyJ1cmwiOiJodHRwczovL3d3dy5lcGhlbWVuZ2luZS5jb20vYXBpL21jcCJ9
Open the link and Cursor adds the server at that address.
ChatGPT
https://www.ephemengine.com/api/mcp
In Settings, enable Developer mode, create an MCP app, and paste this address. Your plan and workspace must allow custom apps.
Codex
codex mcp add caelus --url 'https://www.ephemengine.com/api/mcp'
Run it once, then sign in with codex mcp login caelus if the server asks for an account.

From the project's README

As published by heavyblotto/caelus in README.md.

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

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

Tools it offers (35)

What this server listed when Ahel dialed its public endpoint in Sep 2026, with no key and no account of yours. The names are the server’s own.

natal_chart
current_sky
sky_view
sky_view_sequence
synthetic_validate
synthetic_positions
synthetic_sky_view
transits
synastry
find_aspect_dates
rectification_grid
sky_events
planetary_hours
void_of_course
returns
progressions
composite
dignities
lots
profections
firdaria
releasing
directions
nakshatras
dasha
vargas
yogas
aspect_patterns
parans
chart_signature

Signals

GitHub stars: 1
Forks: 2
Last commit: Oct 2026
Weekly downloads: 66

Advanced

Delivery: caelus-mcp MCP server → your Ahel connector (mcp.ahel.ai) → your AI.
Item type: mcp-server
Key: io-github-heavyblotto-caelus-mcp
Source: github.com/heavyblotto/caelus
Hosted endpoint: https://www.ephemengine.com/api/mcp

github.com/heavyblotto/caelus

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