The NatalChart.AI API is the calculation engine of the NatalChart.AI app, opened to developers. Send a birth date, time and coordinates, get the chart back: no ephemeris files to host, no time-zone tables to maintain, no astrology library to keep up to date.
What you can build
Birth chart pages
Sun, Moon and rising sign, every planet in its sign and house, the aspects with orbs and the element balance, for any birth from 1800 to 2399. /v1/chart/full, /v1/chart/short
Daily horoscopes from the real sky
The day's transits to a person's chart, each with its orb and whether it is building or fading, plus the Moon's phase and the week's sky events. /v1/horoscope/daily, /v1/sky
Compatibility for dating products
Two charts compared: every aspect between them, where each person's planets fall in the other's houses, and a score for each life sphere. /v1/synastry
Forecasts and the year ahead
Every exact transit in a window of up to 92 days, and the solar return chart for any year, at the birth place or wherever the person will be. /v1/transits, /v1/solar-return
Best days
Each day of a window scored for an activity (business, romance, travel, health and more), with the transits for and against it. /v1/timing
Astrocartography and relocation
One city scored against a chart, or the major cities of the world ranked for it, by life sphere and region. /v1/locations/score, /v1/locations/rank
Start in a minute
Create a key (free, no card), then send a birth:
curl https://api.natalchart.ai/v1/chart/short \
-H "Authorization: Bearer $NATALCHART_API_KEY" \
-H "Content-Type: application/json" \
-d '{"birth":{"date":"1991-09-06","time":"18:30","latitude":50.4501,"longitude":30.5234}}'Every endpoint, field and error is in the API documentation, and the OpenAPI document describes them for code generators.
Accuracy you can check
Tropical zodiac, Placidus houses, the five major aspects, true lunar node, positions to four decimals of a degree. The time zone is resolved from the coordinates with the daylight-saving rules of the birth date, and an unknown birth time withholds the houses and angles instead of guessing them. The accuracy report compares the engine with NASA JPL Horizons, and the published demonstration chart lets you check a response before you write any code.
For AI assistants: the MCP server
The same calculations are an MCP server at https://www.natalchart.ai/mcp. Claude, ChatGPT, Cursor and VS Code connect with the same key and call the chart, transit and compatibility tools themselves, so an assistant reads a chart that was computed rather than guessed.
Pricing
| Plan | Price | Requests | Endpoints |
|---|---|---|---|
| Free | $0 | 10 a day | Charts and their parts, daily horoscope, sky, usage |
| API Pro | $6.99 a month | 1,000 a day | Everything: transits, synastry, solar returns, best days, locations |
The pool is per account and refills at 00:00 UTC. A request rejected as invalid is not counted, and birth data is never stored: the log keeps the endpoint, the status and the time only.
Questions
Is there a free astrology API?
Yes. A NatalChart.AI key is free and gives 10 requests a day: natal charts in full or in parts, the daily sky with transits to a chart, and planetary positions for any date. No card is needed. API Pro ($6.99 a month) raises the pool to 1,000 a day and opens transits for a period, synastry, solar returns, best days and astrocartography.
How accurate are the calculations?
Positions come from the Swiss Ephemeris, the standard of professional astrology software, with its data files and the speed flag on. The same engine draws every chart in the NatalChart.AI app, and the accuracy report compares its output with NASA JPL Horizons.
Can I build a horoscope or compatibility app on it?
Yes, that is what it is for: birth chart pages, daily horoscopes from real transits, compatibility scores for dating products, best-day pickers and relocation maps. Commercial use is allowed on both plans; keep the key on your server.
Does it return written interpretations?
No. The API computes and returns numbers: signs, degrees, houses, aspects with orbs, scores per life sphere. There are no AI calls, so the same input always gives the same output, and the words stay yours or your model's.
Which languages and frameworks does it work with?
Anything that can send an HTTPS request with a JSON body: JavaScript, Python, PHP, Swift, Kotlin, no-code tools. The documentation has copy-paste examples, and an OpenAPI document describes every endpoint for code generators.
Can AI assistants use it?
Yes, through the MCP server: Claude, ChatGPT, Cursor and VS Code connect to it with the same key and call the calculations as tools.