auseklis

Astrology MCP server — natal charts, transits, synastry, progressions, returns, eclipses, retrogrades, moon phases. Computed from a real ephemeris, so AI agents stop hallucinating planet positions.

Named after the Latvian morning star. MIT-licensed with no AGPL ephemeris data — see Licensing.

Tools

Plus two prompts (natal_chart_reading, current_sky_report) and a glossary resource (auseklis://glossary).

Features: local birth times with IANA timezones (full historical DST handling) · tropical and sidereal (Lahiri, Fagan/Bradley) zodiacs · whole-sign, equal, Porphyry, and Placidus houses · mean lunar nodes and Black Moon Lilith · Part of Fortune (classical day/night formula).

Related MCP server: Precision astronomical ephemeris and planetary positions via the Swiss Ephemeris.

Installation

Claude Code

claude mcp add auseklis -- npx -y auseklis

Claude Desktop / any MCP client (stdio)

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

No API keys, no configuration — the ephemeris is computed locally.

Desktop Extension

Download auseklis.mcpb from the releases page and double-click to install in Claude Desktop. Or build it yourself: npm run bundle.

Remote (self-hosted)

The same server runs as a Cloudflare Worker speaking Streamable HTTP. Deploy it to your own account:

npm run deploy   # wrangler deploy
claude mcp add --transport http auseklis https://auseklis.<your-subdomain>.workers.dev/mcp

Set the MCP_SHARED_SECRET secret to require a bearer token.

Library usage

The ephemeris core (everything under src/ephemeris/) is importable directly — no MCP client or subprocess needed. This is the right shape for serverless runtimes (Vercel, Workers), where spawning npx auseklis per request is not an option:

import { computeNatalChart } from "auseklis/ephemeris";
import { findRetrogradePeriods } from "auseklis/ephemeris/events";
import { findEclipses } from "auseklis/ephemeris/eclipses";

const chart = computeNatalChart({
  utc: "1990-03-15T13:45:00Z",
  location: { latitude: 56.95, longitude: 24.11 }, // Riga
  houseSystem: "placidus",
});

auseklis/ephemeris carries the chart math (natal, transits, synastry, composite, progressions, single positions, angles) plus resolveInstant for local-time → UTC conversion; …/events and …/eclipses carry the time-domain searches. Fully typed, ESM only, no data files.

Example questions to ask

• "Compute my natal chart — born 15 March 1990, 15:45 in Riga."

• "What's transiting my Sun this month?"

• "When exactly is my Saturn return?"

• "Synastry between me and my partner?" (two birth date/times)

• "When is Mercury retrograde in 2027, and in which signs?"

• "Is tonight's full moon visible as an eclipse from here?"

The model handles place-name → coordinates; the server handles local-time → UTC via the IANA timezone database.

Accuracy

Positions come from astronomy-engine (VSOP87 + NOVAS C 3.1): ±1 arcminute for 1700–2200, far below the 1° resolution astrological interpretation uses. Event searches (stations, ingresses, returns, quarters) are refined to ~1 second of time. Verified in CI against published eclipse dates, the 2026 equinox, NOVAS Sun positions, and an independent Placidus implementation.

Architecture

src/
├── ephemeris/        Astrology core — backend-agnostic
│   ├── engine.ts     EphemerisBackend interface + astronomy-engine adapter (the swap seam)
│   ├── index.ts      Charts, aspects, synastry, composite, progressions
│   ├── events.ts     Time searches: returns, stations, ingresses, aspect times, moon phases
│   ├── eclipses.ts   Eclipse searches with astrological context
│   ├── houses.ts     Whole-sign, equal, Porphyry, Placidus (semi-arc solver)
│   ├── points.ts     Mean lunar nodes, Black Moon Lilith
│   ├── sidereal.ts   Ayanamsa (Lahiri, Fagan/Bradley)
│   └── time.ts       IANA timezone → UTC conversion (no dependencies, uses Intl)
├── mcp/              Tool/prompt/resource definitions on @modelcontextprotocol/sdk
├── stdio.ts          Local entry — `npx auseklis`
└── index.ts          Remote entry — Cloudflare Worker, Streamable HTTP via @hono/mcp

The EphemerisBackend interface in engine.ts is the deliberate swap seam: a future Rust/WASM clean-room ephemeris only needs to reimplement that one interface.

Development

npm install
npm run typecheck   # strict TS
npm test            # 23-check smoke suite (ephemeris references + MCP end-to-end)
npm run build       # emit dist/
npm run dev         # local Cloudflare Worker on :8787
npx @modelcontextprotocol/inspector node dist/stdio.js   # poke tools interactively

See docs/tools.md for the full tool reference and docs/architecture.md for design notes.

Licensing

MIT. This project deliberately avoids the Swiss Ephemeris (.se1/.se2 data files and the sweph bindings): those are AGPL-licensed, which would impose AGPL obligations on any network service built on them. Everything here is computed from MIT-licensed code with no external data files — safe to embed, fork, and deploy commercially. Details in NOTICE.

The trade-off: no Chiron or asteroids (they need ephemeris data files). They are on the roadmap via public-domain JPL-derived data.

Roadmap

• v1: Rust/WASM clean-room ephemeris backend behind the same EphemerisBackend seam

• Chiron + major asteroids from public-domain JPL data

• Koch houses, declination/parallel aspects