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Black Moon Lilith calculator - mean and true lunar apogee in the natal chart

post_astrology_lilith
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Calculate mean and true Black Moon Lilith for a birth chart, returning zodiac sign, degree, house, daily speed, retrograde flag, and interpretation.

Instructions

Calculate Black Moon Lilith for any birth chart, both the mean lunar apogee, the steady and most widely used point, and the true or osculating apogee, the exact position that can shift sign and turn retrograde. Returns the zodiac sign, degree, house, ecliptic longitude and latitude, daily speed, retrograde flag, and a plain language interpretation for each variant. Built for natal astrology apps and AI agents exploring the wild, suppressed, and reclaimed self that Lilith represents.

Input Schema

NameRequiredDescriptionDefault
dateYesBirth date in YYYY-MM-DD format. Determines planetary positions for the specific calendar day.
langNoResponse 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
timeYesBirth time in 24-hour HH:MM:SS format. Determines the Ascendant (rising sign) and house cusps. Use 12:00:00 if unknown.
compactNoSet 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.
latitudeYesBirth location latitude in decimal degrees (-90 to 90). Positive = North, negative = South.
nodeTypeNoLunar 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
timezoneYesTimezone: 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.
longitudeYesBirth location longitude in decimal degrees (-180 to 180). Positive = East, negative = West.
houseSystemNoHouse system used to place each Lilith variant in a house. Placidus (default), Whole Sign, Equal, or Koch.placidus

Output Schema

NameRequiredDescriptionDefault
lilithYes
summaryYes
houseSystemYes
birthDetailsYes

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed2 schema fields changedv1.1.2
    • changedInput schema / examples
      Previous value: -[
-  {
-    "date": "1990-07-15",
-    "latitude": 40.7128,
-    "longitude": -74.006,
-    "time": "14:30:00",
-    "timezone": -5
-  }
-]New value: +[
+  {
+    "date": "1990-07-15",
+    "latitude": 40.7128,
+    "longitude": -74.006,
+    "time": "14:30:00",
+    "timezone": "America/New_York"
+  }
+]
    • changedInput schema / properties / timezone / example
      Previous value: --5New value: +"America/New_York"
  2. First observedv0.1.0

TDQS

A3.5/5.0
Behavior3/5

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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the safety profile is covered. The description adds the mean-vs-true distinction and notes that the true apogee can shift sign and turn retrograde, but says nothing about permissions, rate limits, or precision caveats beyond that. Adequate but not rich.

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?

Three sentences, front-loaded with the core action and resource, then the variant distinction, then the return fields and audience. Dense but every sentence carries information; only the audience sentence is borderline expendable.

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?

With an output schema present, the description needn't enumerate return values, and the parameter documentation is fully covered by the schema. For a complex calculation tool this is nearly complete; the only gap is any guidance on choosing this over a broader natal-chart tool.

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

Parameters3/5

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

Schema description coverage is 100%, so the schema already documents all nine parameters in depth; baseline 3 applies. The description's explanation of the mean/true variants loosely maps to nodeType, but adds no syntax or format detail the schema lacks.

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

Purpose4/5

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

The description names a specific verb and resource ('Calculate Black Moon Lilith for any birth chart') and precisely scopes it to both the mean and true lunar apogee. It clearly identifies the tool's domain, though it never explicitly contrasts itself with overlapping siblings like post_astrology_natal_chart or post_astrology_asteroids, which may also surface points.

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

Usage Guidelines3/5

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

Usage is implied ('for any birth chart') and the audience is named ('natal astrology apps and AI agents'), but there is no explicit when-to-use/when-not guidance or routing to alternatives. An agent can infer the context but gets no exclusions or prerequisites.

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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