Click on "Deploy Server".
Wait a few minutes for the server to deploy. Once ready, it will show a "Started" state.
In the chat, type @ followed by the MCP server name and your instructions, e.g., "@mcp-ephemeris What's the moon phase today?"
That's it! The server will respond to your query, and you can continue using it as needed.
Here is a step-by-step guide with screenshots.
The real sky, for your AI. An MCP server that gives any assistant (Claude, Cursor, agents) computed planetary positions — never guessed — powered by the Swiss Ephemeris engine, and validated against JPL Horizons (NASA) to under one arcsecond.
Cardinal rule: the LLM never computes. This server is a facade over an ephemeris engine. The model interprets; the sky is a fact.
(Version française : https://llmastro.com/notre-moteur)
Open Settings → Developer → Edit Config, then add:
{
"mcpServers": {
"llmastro": {
"command": "npx",
"args": ["-y", "@cosmosos/mcp-ephemeris"]
}
}
}Fully quit Claude Desktop (system tray) and relaunch it. Then ask: "What's the moon phase today?" — Claude calls the server and answers from genuinely computed positions.
Cursor / Windsurf / others: add the same llmastro entry
(command: npx, args: ["-y", "@cosmosos/mcp-ephemeris"]) to your client's MCP
configuration.
Related MCP server: auseklis
19 tools, all backed by the same server-side computed engine.
Tool | Input | Output |
|
| ecliptic positions of all bodies (sign, degree, retro) |
|
| moon phase, illumination %, description |
|
| the sky right now (current transits) for a place |
|
| grid of major + minor aspects between bodies |
Tool | Input | Output |
| birth + | full chart: houses, aspects, ASC/MC, moon phase, Hermetic Lots |
| birth + optional | transit→natal aspects, sorted by orb |
| two births | inter-chart aspects + harmony/tension summary |
| two births | midpoint composite chart |
| birth + | progressed positions ("a day for a year") |
| birth + | instant + chart of the solar return |
| birth + optional | instant + chart of the next lunar return |
Tool | Input | Output |
|
| sign-change dates (retrograde-robust) |
|
| retrograde/direct stations over the range |
|
| magnitude, obscuration, Saros of a known eclipse (swisseph) |
|
| next/previous eclipse: maximum, type, contacts (swisseph) |
Tool | Input | Output |
|
| planetary MC/IC lines + parans (crossings) |
|
| life-path number (numerology) |
| — | active engine, native addon load status, real precision |
|
| delta of our positions vs JPL Horizons (NASA) in arcseconds — network required |
(swisseph) = requires the native Swiss Ephemeris addon; returns null on the AstraCore fallback.
Under Swiss Ephemeris, positions match the world reference JPL Horizons (NASA) to under one arcsecond (measured 2026-07-19):
Body | Difference vs NASA |
Sun | 0.2″ |
Moon | 1.5″ |
Jupiter | 0.1″ |
Pluto | 0.4″ |
Check it yourself with the validate_against_horizons tool.
Computation is routed by the ASTRO_ENGINE variable:
swisseph (default) — Swiss Ephemeris, native addon, sub-arcsecond
precision. Compiles automatically wherever a C++ build chain is present
(Linux, macOS, most servers).
astracore — in-house pure-TypeScript engine (VSOP/Meeus), no native
binary. Used as an automatic fallback when swisseph couldn't be compiled
(common on Windows). Sun and Moon stay accurate; outer planets drift by a few
arcminutes.
To force an engine: ASTRO_ENGINE=swisseph or ASTRO_ENGINE=astracore.
The server runs on your machine: your birth data is sent nowhere. Only
validate_against_horizons makes an outbound request (to NASA's public API).
Node.js ≥ 20.
For maximum precision (swisseph): a C++ build chain (python3, make, a
compiler) on the machine. Otherwise, automatic fallback to astracore, with
no configuration.
Powered by the astrology engine of Llmastro. Learn more about the precision and architecture: https://llmastro.com/notre-moteur.
Free for non-commercial use (personal, research, education, non-profit organizations) — under the PolyForm Noncommercial 1.0.0 license.
Commercial / professional use: a paid license is required. To obtain one, contact KAIROSAST LTD via https://llmastro.com/contact.
Note: the optional swisseph dependency (Swiss Ephemeris, Astrodienst) has its
own license (AGPL or a commercial Swiss Ephemeris license) and is not covered by
this one. Professional use must comply with it separately.
This repository is self-contained: the ephemeris engine is vendored in
vendor/ephemeris/ (source), and the build inlines it into dist/ via
tsup.
pnpm install # or npm install
pnpm build # bundles dist/index.js (engine inlined)
pnpm start # runs the MCP server (stdio) locallyDefault engine: swisseph (sub-arcsecond precision) if the native addon
compiles, otherwise automatic fallback to astracore (pure TypeScript, no
binary). Force via ASTRO_ENGINE=swisseph|astracore.
The vendored engine is a snapshot of @astro-platform/ephemeris (Llmastro),
re-synced manually.
Aspects (majeurs et mineurs) entre les planètes à un instant donné, avec orbe et tonalité. Grille d'aspects calculée par le moteur, pas estimée.
Inputs: datetime (required).
Thème composite par mi-points : pour chaque corps, le point milieu circulaire entre les deux thèmes (convention Robert Hand). Représente la relation elle-même.
Inputs: personA (required), personB (required).
Le ciel à l'instant présent (transits du moment) pour un lieu donné : positions en maisons + aspects.
Inputs: latitude (required), longitude (required).
Détail d'une éclipse (magnitude, obscuration, type, série de Saros) pour une date d'éclipse connue. Nécessite le moteur swisseph (retourne null en mode AstraCore).
Inputs: kind (required), datetime (required).
Phase de la Lune (nom, illumination %, description) à un instant donné, dérivée de la position réelle Soleil/Lune.
Inputs: datetime (required).
Thème natal complet : positions en maisons, aspects, ASC/MC, phase lunaire, Lots hermétiques. Prend une date/heure LOCALE + fuseau IANA + coordonnées. Zodiaque tropical (défaut) ou sidéral (Lahiri), et système de maisons au choix (Placidus par défaut).
Inputs: date (required), time (required), latitude (required), timezone (required), +3 more.
Positions écliptiques géocentriques de tous les corps (Soleil→Pluton, nœuds, Lilith) à un instant donné. Calculé côté serveur par le moteur d'éphéméride — jamais estimé par le modèle.
Inputs: datetime (required).
Progressions secondaires (méthode « un jour après la naissance = une année de vie ») : positions planétaires progressées à une date cible. La Lune progressée (~1 signe / 2,5 ans) est la plus lue.
Inputs: date (required), time (required), latitude (required), timezone (required), +2 more.
Retour solaire d'une année donnée : l'instant exact où le Soleil retrouve sa longitude natale, et le thème dressé à cet instant (pour le lieu de résidence si fourni, sinon lieu de naissance).
Inputs: date (required), time (required), year (required), latitude (required), +4 more.
Synastrie : aspects inter-thèmes entre deux personnes (planètes A × planètes B), triés par orbe, avec un résumé harmonie/tension. Réutilise la table d'aspects canonique du moteur.
Inputs: personA (required), personB (required).
Transits croisés au thème natal : aspects entre les planètes qui transitent (aujourd'hui ou à une date donnée) et les planètes de naissance, triés par orbe. Le cœur des « prévisions ».
Inputs: date (required), time (required), latitude (required), timezone (required), +2 more.
Recent tool additions, removals, and schema changes observed during successful MCP inspections.
Loading tool schema changelog…
Scored across 11 tools
Each tool has a clearly distinct purpose: positions, moon phase, sky, aspects, natal chart, transits, solar return, eclipses, synastry, composite chart, and secondary progressions. No two tools do the same thing; even overlapping concepts like aspects are scoped differently (general vs. transits vs. synastry).
All tool names follow the consistent pattern 'get_<topic>', with clear and descriptive suffixes (e.g., get_planet_positions, get_moon_phase). No mixing of conventions like camelCase or different verb styles.
With 11 tools, the set covers core ephemeris and astrology functionality without being overwhelming. Each tool earns its place, providing a well-scoped range from basic positions to advanced charts like synastry and secondary progressions.
The tool surface covers the full lifecycle of ephemeris queries: positions, aspects, moon phase, multiple chart types (natal, solar return, composite), transits, progressions, synastry, and eclipses. Missing features like asteroids or harmonic charts are non-essential for a general service.
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