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Generate natal chart - Birth chart calculator API with houses and aspects

post_astrology_natal_chart

Read-only

Calculate a complete Western natal chart from birth date, time, and location. Returns planets, houses, aspects, and Ascendant for astrology apps and birth chart generators.

Instructions

Calculate complete Western astrology natal chart (birth chart) with tropical zodiac. Returns all 14 celestial bodies (the 10 classical planets Sun through Pluto, the lunar nodes, Chiron, and Black Moon Lilith), 12 house cusps with customizable house systems (Placidus, Whole Sign, Equal, Koch), major and minor aspects, Ascendant, Midheaven, dominant elements and modalities. Perfect for astrology apps, birth chart generators, horoscope websites, and astrological consultation tools. Verified against NASA JPL Horizons.

Input Schema

TableJSON Schema

Name	Required	Description	Default
`date`	Yes	Birth date in YYYY-MM-DD format. Determines planetary positions for the specific calendar day.
`lang`	No	Response language (BCP 47). Supported: en, tr, de, es, hi, pt, fr, ru, zh-Hans, zh-Hant. Defaults to en. Coverage varies by domain, and a field with no translation in the requested language returns English.	en
`time`	Yes	Birth time in 24-hour HH:MM:SS format. Determines the Ascendant (rising sign) and house cusps. Use 12:00:00 if unknown.
`compact`	No	Set true for the same data in a compact shape: arrays of same-shaped objects arrive columnar as {"__cols":[names],"__rows":[[values]]}. Lossless, typically 40 to 52 percent fewer tokens.
`latitude`	Yes	Birth location latitude in decimal degrees (-90 to 90). Positive = North, negative = South.
`nodeType`	No	Lunar node convention. "mean" is the smoothed average node, which always moves retrograde; "true" is the osculating node, which tracks the real perturbed node, oscillates up to about 1.5 degrees either side of the mean on a 173-day cycle, and can briefly turn direct. Neither is more correct and they almost always fall in the same sign. Applies to the North and South Node. True is the osculating node and the default, because it is what most Western chart software reports; mean is the smoothed node preferred by several evolutionary schools, so pass "mean" to match one. Nothing else in the chart changes, and the two agree on the sign except when the node sits within about 1.8 degrees of a cusp. Defaults to "true".	true
`timezone`	Yes	Timezone: an IANA name (e.g. "America/New_York", "Europe/London", or `cities[0].timezone` from /location/search) or decimal hours from UTC (e.g. -5 for EST, 5.5 for IST). An IANA name is resolved to the offset in force at the given date and time.
`longitude`	Yes	Birth location longitude in decimal degrees (-180 to 180). Positive = East, negative = West.
`houseSystem`	No	House system for dividing the chart into 12 houses. Placidus (default) is most popular in Western astrology and time-sensitive. Whole Sign assigns one sign per house (simpler, ancient). Equal houses divide chart into 30° segments from Ascendant. Koch emphasizes houses in high latitudes.	placidus

Output Schema

TableJSON Schema

Name	Required	Description	Default
`houses`	Yes
`vertex`	Yes
`aspects`	Yes
`planets`	Yes
`summary`	Yes
`patterns`	No
`ascendant`	Yes
`midheaven`	Yes
`houseSystem`	Yes
`birthDetails`	Yes
`partOfFortune`	Yes
`aspectsInterpretation`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.1.0Oct 4, 2026

TDQS

A4.3/5.0

Behavior4/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already mark readOnlyHint=true and destructiveHint=false, so safety is covered. The description adds behavioral context: mentions 'Verified against NASA JPL Horizons' for accuracy, lists output scope (14 bodies, 12 houses, aspects), and clarifies return items like Ascendant and dominants. This adds value beyond annotations.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is rich but efficient, with key output and use-case information front-loaded. It doesn't waste words, though it's longer than strictly necessary. Still, it's well-structured for an agent to quickly grasp scope.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the tool's complexity (9 params, output schema), the description covers scope well but could add more on output structure or edge cases (e.g., what happens with invalid dates). However, the output schema is present, so return details are likely covered. Doesn't mention error handling or prerequisites beyond timezone.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, so parameters are well-documented. The description doesn't add much on top for most params, but it does hint at house systems and body lists. However, it lacks details on optional params like lang and compact. Given high coverage, this is above baseline but not perfect.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states 'Calculate complete Western astrology natal chart (birth chart) with tropical zodiac' and lists specific outputs like celestial bodies, house cusps, and aspects. It distinguishes itself from sibling tools like individual planet or house tools by mentioning the full chart calculation.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description implies when to use: for full birth chart needs. It doesn't explicitly mention when not to use or point to alternatives, but given the sibling list, it's clear this is the comprehensive chart tool while others are focused (e.g., post_astrology_houses for houses only).

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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