Falcı Hatun — Astrology & Tarot Engine

An OKX.AI A2MCP service. It returns facts, not prose — because the agent calling it is already a language model.

Most "AI astrology" products bolt an LLM onto a vague prompt and let it improvise the sky. This one does the opposite. Falcı Hatun computes the chart with a real ephemeris and hands the agent structured truth: every planet's longitude, sign, house and retrograde state; every aspect with its orb; every transit bisected to the exact moment it perfects; the drawn cards and their meanings.

The agent writes the reading. That split is the whole design — and it means this service needs no LLM of its own: no API key, no vendor bill, no rate limit, and an answer that is byte-identical every time you ask.

Agent  →  "birth data"  →  Falcı Hatun  →  the actual sky  →  Agent writes the reading

Tools

Chart engine: astronomy-engine (JPL-grade positions) + luxon (IANA timezone rules, so historical DST is handled rather than assumed). House system: Equal — stated in the response, because a chart that hides its house system cannot be verified.

Related MCP server: Astro MCP Server

Bilingual by construction

This grew out of a Turkish app, and OKX.AI is a global marketplace. A tool that answers "Kılıç Dokuzlusu: kaygı, endişe, uykusuzluk" to an English-speaking agent has not really answered.

So nothing is replaced — everything is doubled. Every sign, planet, aspect, spread position and card meaning ships in both languages on the same response:

{ "name": "Boğa",           "en": "Taurus", "element": "toprak", "elementEn": "earth" }
{ "name": "Kılıç Dokuzlusu", "nameEn": "Nine of Swords",
  "meaning":   "kaygı, endişe, uykusuzluk, kabuslar",
  "meaningEn": "anxiety, worry, sleeplessness, nightmares" }

The agent replies in whichever language the person used — the MCP instructions tell it so. All 78 cards, both orientations, are covered; a test asserts there are no gaps. Turkish stays first-class: it is the original, and it is the market this was built for.

What was fake, and what is real now

This engine grew out of Falcı Hatun, a shipped Turkish astrology app. Porting it surfaced two features that were not doing what they claimed.

Compatibility was a hash of the partner's name.

const seed = hash(partner.name + partner.date);
emotional:     40 + (seed % 60),
communication: 40 + ((seed >> 3) % 60),
attraction:    40 + ((seed >> 6) % 60),

Change one letter of the name and "emotional compatibility" moved. Neither chart was ever consulted. synastry now computes actual cross-aspects — Venus to Mars, Moon to Saturn, the whole grid — weighted by classical significators and orb exactness. There is a test that asserts renaming a person does not move the score, and that changing their birth date does.

The transit timeline was six hardcoded events.

{ days: 7,  title: 'Merkür Retrosu Başlıyor' }
{ days: 14, title: 'Boğa Burcunda Dolunay' }

Fixed offsets from today, identical for every user. Mercury was not necessarily stationing; the Moon was not necessarily full; nobody's chart was involved. sky_ahead and transits now search the ephemeris and bisect to the exact moment — and a test checks that consecutive new moons come out one synodic month apart (~29.53 days), which a hardcoded list could never satisfy.

It tells you what it doesn't know

A reading that looks authoritative and is quietly wrong is worse than no reading.

Unknown birthplace → error, not a guess. The original silently fell back to { lat: 39.0, lon: 35.0 } — the geographic centre of Turkey — for any city it didn't recognise. The ascendant and every house cusp depend on latitude and longitude, so an unrecognised birthplace produced a confident, wrong chart. Now it raises UnknownPlaceError and suggests near-matches. Explicit latitude/longitude work anywhere on Earth.

No birth time → the chart says so. Without a time, the ascendant, the midheaven and every house placement rotate a full circle every 24 hours. Falcı Hatun still returns the chart, but the caveats field states plainly which parts are unusable, and the MCP instructions tell the calling agent not to speak about them. Transits to the Ascendant are omitted entirely rather than invented.

A dimension with no planetary contacts scores null, not a number. If two people have no Moon–Venus contact, the emotional score is absent — not filled in with something plausible.

Run it

npm install
npm test        # 60 assertions
npm run dev     # http://localhost:8788/mcp

Deploy

vercel --prod

Your MCP endpoint is https://<your-domain>/api/mcp — that HTTPS URL is what you register with OKX.AI.

Call it

curl -X POST https://<your-domain>/api/mcp \
  -H 'Content-Type: application/json' \
  -d '{"jsonrpc":"2.0","id":1,"method":"tools/call","params":{
        "name":"natal_chart",
        "arguments":{"date":"1990-05-15","time":"09:30","place":"İzmir"}}}'

{
  "sun":    { "name": "Boğa",  "degree": 24.17, "element": "toprak" },
  "moon":   { "name": "Oğlak", "degree": 12.4 },
  "rising": { "name": "Yengeç" },
  "planets": [
    { "name": "Merkür", "sign": { "name": "Boğa" }, "house": 10, "retrograde": true },
    { "name": "Plüton", "sign": { "name": "Akrep" }, "house": 5, "retrograde": true }
  ],
  "aspects": [
    { "from": "Güneş", "to": "Ay", "aspectTr": "üçgen", "orb": 0.16, "exactness": 0.977 }
  ],
  "houseSystem": "equal",
  "caveats": []
}

Pricing

Free.

Relationship to the Falcı Hatun app

This is a separate, standalone service. The mobile app is untouched — its Cloudflare Worker, its prompts and its reading flows are not used, not called, and not modified. What was carried over is the data layer (the 78-card Turkish deck, the zodiac table, the city coordinates) and the astrology mathematics, rebuilt for Node and corrected where it was wrong.

MIT.