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Composite Chart - Midpoint relationship chart with interpretations

post_astrology_composite_chart

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Calculate a composite chart from two birth charts using midpoints to reveal a relationship's identity, emotional bond, communication style, and growth direction as one entity.

Instructions

Generate a composite chart by calculating midpoints between two natal charts. The composite chart represents the relationship as a single entity, showing its core identity, emotional bond, communication style, and growth direction. Uses the midpoint method: planets, angles and house cusps are each the midpoint of the two natal values, so the Ascendant always sits on the first cusp. Returns composite planetary positions, house cusps, Ascendant, Midheaven, aspects, and relationship interpretation. Composite chart API, midpoint chart calculator, relationship astrology, couple chart analysis.

Input Schema

Name	Required	Description	Default
`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
`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.
`person1`	Yes	First person birth details (date, time, location, timezone).
`person2`	Yes	Second person birth details (date, time, location, timezone).
`houseSystem`	No	House system for the composite chart. Placidus (default), Whole Sign, Equal, or Koch.	placidus

Output Schema

Name	Required	Description	Default
`aspects`	Yes
`person1`	Yes
`person2`	Yes
`interpretation`	Yes
`compositeHouses`	Yes
`compositePlanets`	Yes
`compositeAscendant`	Yes
`compositeMidheaven`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

Changed3 schema fields changedv1.1.2Oct 5, 2026

changedInput schema / examples

Previous value: -[
-  {
-    "person1": {
-      "date": "1990-07-15",
-      "latitude": 40.7128,
-      "longitude": -74.006,
-      "time": "14:30:00",
-      "timezone": -5
-    },
-    "person2": {
-      "date": "1990-07-15",
-      "latitude": 40.7128,
-      "longitude": -74.006,
-      "time": "14:30:00",
-      "timezone": -5
-    }
-  }
-]New value: +[
+  {
+    "person1": {
+      "date": "1990-07-15",
+      "latitude": 40.7128,
+      "longitude": -74.006,
+      "time": "14:30:00",
+      "timezone": "America/New_York"
+    },
+    "person2": {
+      "date": "1990-07-15",
+      "latitude": 40.7128,
+      "longitude": -74.006,
+      "time": "14:30:00",
+      "timezone": "America/New_York"
+    }
+  }
+]

changedInput schema / properties / person1 / properties / timezone / example
```
Previous value: --5New value: +"America/New_York"
```
changedInput schema / properties / person2 / properties / timezone / example
```
Previous value: --5New value: +"America/New_York"
```

First observedv0.1.0Oct 4, 2026

TDQS

B3.4/5.0

Behavior4/5

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 genuine behavioral context beyond that: the exact midpoint methodology ('planets, angles and house cusps are each the midpoint of the two natal values'), the invariant that the Ascendant always sits on the first cusp, and the returned artifacts. No auth or rate-limit context, but the calculation semantics are well disclosed.

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

Conciseness3/5

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

The purpose and method are front-loaded well, but the closing keyword list ('Composite chart API, midpoint chart calculator, relationship astrology, couple chart analysis') is SEO padding that adds no actionable information, and 'core identity, emotional bond, communication style, and growth direction' is marketing-flavored filler.

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 need not enumerate return values, and it still summarizes them. For a 5-parameter, nested-object tool with full schema coverage, the only real gap is the absence of when-to-use guidance relative to the synastry/compatibility siblings.

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%, with person1/person2 sub-fields, lang, compact, and houseSystem all documented in the schema itself. The description adds no parameter-level meaning (e.g., it never mentions houseSystem or the lang/compact options), so the baseline 3 for fully-covered schemas applies.

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?

States a specific verb and resource ('Generate a composite chart by calculating midpoints between two natal charts') and explains the underlying method in detail, so the agent knows exactly what computation is performed. However, it never names its closest sibling (post_astrology_synastry), leaving the composite-vs-synastry distinction to be inferred from the description of the composite as 'a single entity'.

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

Usage Guidelines2/5

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

The description explains what a composite chart represents but gives no explicit when-to-use guidance, no conditions, and no alternatives. An agent choosing between this and post_astrology_synastry or post_astrology_compatibility_score gets no routing help beyond the implicit 'relationship' framing.

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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