Accurate natal charts inside your AI assistant
Language models guess where the planets were. They often get the rising sign, the Moon and historical daylight saving time wrong. This server lets ChatGPT, Claude and any MCP client compute the chart instead, with the same engine as natalchart.co.
Free. No account, no API key, nothing to download. Birth data is computed on the fly and never stored (privacy).
Can ChatGPT read my birth chart?
ChatGPT can help explain supplied birth-chart data, but it should not guess the chart from a birth date, time and place. Calculate it first with an ephemeris, then give the assistant the placements it should interpret. The assistant can still misread them: astrological interpretation is symbolic, not a factual prediction or a validated assessment of a person.
- Calculate the chart. Use the free birth chart calculator, enter the birthplace and the exact local birth time when it is known, then open the full interactive chart.
- Supply the displayed placements you want discussed. Start with the Sun, Moon and Ascendant when available. Add any selected planet's sign, degree and house, the listed aspects and orbs, and the house system shown by the chart. Copy those entries manually rather than asking the model to reconstruct them.
- Ask for interpretation, not recalculation. Tell the assistant to use those values exactly, keep calculated facts separate from symbolic interpretation and preserve every uncertainty note.
Paste the chart data after this prompt:
Interpret the calculated birth-chart data below without recalculating it.
Keep positions, houses, degrees and aspects separate from symbolic interpretation.
If present, state the house system shown, preserve any uncertainty notes, and do not invent missing data or predict outcomes.
[Paste the calculated chart data here]If the birth time is unknown
Mark it as unknown instead of choosing a plausible hour. Natal Chart uses 12:00 local time as a reference for planetary positions, leaves out the Ascendant, Midheaven and houses, and flags when the Moon may have changed sign during that local calendar day. An AI assistant should preserve those limits rather than infer the missing angles.
If the assistant already has this MCP server connected, it can call calculate_natal_chart first and interpret the returned data in the same way. In the manual workflow, the assistant does not need a name or the raw birth details once the placements have been calculated. Read how the browser calculator and the MCP service handle birth data in the privacy policy.
Connect it
Claude (web, desktop and mobile, free plan included)
Settings → Connectors → Add custom connector. Name it “Natal Chart” and paste https://natalchart.co/mcp. No authentication.
ChatGPT
Plans that allow custom connectors: turn on developer mode, create a connector with the URL https://natalchart.co/mcp and no authentication.
Le Chat, Perplexity and other assistants
Wherever the assistant lets you add a remote MCP server or custom connector by URL, use https://natalchart.co/mcp (Streamable HTTP, no auth).
Claude Code, Cursor and other developer tools
claude mcp add --transport http natalchart https://natalchart.co/mcp{
"mcpServers": {
"natalchart": { "url": "https://natalchart.co/mcp" }
}
}What it can do
| Tool | What it answers |
|---|---|
calculate_natal_chart | Planetary signs, degrees and retrograde status; houses, Ascendant, Midheaven, and traditional and modern chart rulers when birth time is known; Placidus by default, with Whole Sign on request or as a polar fallback; major aspects with orbs, Chiron within the supported ephemeris range, Lilith and the lunar nodes, element balance, a written reading in English, Spanish, Italian or French, and a link to the interactive chart wheel. Try the chart ruler calculator or Chiron sign-and-house verifier in the browser without a custom connector. |
get_planet_positions | Where every planet is right now or on any date, and which ones are retrograde. “Is Mercury retrograde?” gets a computed answer. |
compare_charts | Synastry between two people: both Big Threes and every aspect between their planets, sorted by how tight it is. |
Try asking
- “What’s my natal chart? I was born on 2 November 1987 at 6:15 in Valladolid, Spain.”
- “What is my rising sign if I was born at 23:40 on 14 March 1995 in Manchester?”
- “Is Mercury retrograde this week?”
- “How compatible are we? Me: 3 May 1990, Rome. Him: 21 January 1988, 14:10, Milan.”
Why the numbers are right
- Planet positions come from an astronomical ephemeris (VSOP87 and analytic lunar theory via astronomy-engine), not from memory.
- Local birth time is converted to UTC with the IANA time zone database, including historical daylight saving rules. Madrid in 1962 and Madrid in 2026 are not the same offset.
- Tropical zodiac, geocentric apparent positions, Placidus houses (whole sign above the polar circles), mean nodes and mean Lilith. Chiron from a JPL Horizons table.
- If the birth time is unknown, houses and the Ascendant are left out instead of invented, and a Moon sign change during that day is flagged.
Plain HTTP API
The same calculations are available as JSON, documented in OpenAPI:
curl "https://natalchart.co/api/v1/natal-chart?birth_date=1987-11-02&birth_time=06:15&birth_place=Valladolid,%20Spain&language=en"
curl "https://natalchart.co/api/v1/sky"Fair use please. If you show results, link to natalchart.co.