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ephemeris_composite

Read-only

Derive a relationship chart by computing the midpoints of planet pairs from two natal charts. Input birth details for each person to obtain the composite astrological chart.

Instructions

Calculate a composite chart from two or more natal charts. The composite uses midpoints of each planet pair to derive a single relationship chart.

CREDIT COST: 3 credits per call.

EXAMPLE: Composite for two people: person_a_datetime='1990-04-15T14:30:00', person_a_latitude=41.88, person_a_longitude=-87.63, person_b_datetime='1988-09-22T08:15:00', person_b_latitude=34.05, person_b_longitude=-118.24

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
person_a_datetimeYesPerson A birth datetime (ISO 8601).
person_a_timezoneNoIANA timezone name for Person A, e.g. 'America/Denver'.
person_a_latitudeYesPerson A birth latitude.
person_a_longitudeYesPerson A birth longitude.
person_b_datetimeYesPerson B birth datetime (ISO 8601).
person_b_timezoneNoIANA timezone name for Person B, e.g. 'Europe/London'.
person_b_latitudeYesPerson B birth latitude.
person_b_longitudeYesPerson B birth longitude.
formatNoUse 'llm' for token-efficient LLM projection.
Behavior4/5

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

Annotations already indicate readOnlyHint=true and destructiveHint=false, and the description adds credit cost (3 credits per call), providing useful behavioral context beyond the annotations. However, it does not address auth or rate limits.

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 concise, front-loading the purpose in the first sentence, followed by credit cost and an example. It is well-structured with minimal verbosity.

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

Completeness2/5

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

The description claims the tool handles 'two or more' charts, but the input schema only supports two persons (a and b), leaving a gap. No output schema is provided, and the description does not explain how to handle more than two charts. This inconsistency reduces completeness.

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 coverage is 100%, so each parameter has a description. The description adds an example but no new semantic detail beyond what the schema provides. Baseline score of 3 is appropriate.

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 the tool calculates a composite chart from natal charts using midpoints, which is a specific verb and resource. It differentiates from siblings like 'ephemeris_composite_midpoint' by focusing on the composite calculation itself.

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?

The description gives an example of usage but does not explicitly state when to use this tool versus alternatives (e.g., synastry or overlay). No guidance on prerequisites or limitations is provided.

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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