Composite Chart

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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false, and openWorldHint=false, so the safety profile is covered. The description adds meaningful behavior beyond that by explaining the midpoint-averaging method and the cost of 50 credits (Tier 3), which an agent needs for planning and budgeting.

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

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

The description is front-loaded with the core calculation in one sentence, followed by compact grouped metadata for group, endpoint, required fields, and cost. There is no redundant prose, and each line adds practical information for invocation or planning.

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

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

Given the rich nested input schema, existing output schema, and safety annotations, the description covers the essential purpose, required inputs, endpoint, and cost. The main missing context is sibling differentiation—why an agent should pick this composite tool over Davison, coalescent, or synastry—which keeps it from a 5.

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

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

Schema description coverage is 100%, and the nested chart1/chart2 schemas contain extensive guidance on date, time, timezone, coordinates, and house systems. The description only repeats that chart1 and chart2 are required, so it does not add semantic value beyond the schema; baseline 3 is appropriate.

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

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

The description gives a specific verb and resource: it states that the tool calculates a midpoint composite chart by averaging planetary positions and house cusps from two natal charts. That is much clearer than a tautology, but it does not explicitly differentiate this tool from nearby siblings such as astroway_relational_davison, astroway_relational_coalescent, or astroway_relational_synastry.

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

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

The description lists required inputs, endpoint, and cost, but it gives no guidance on when to choose a composite chart rather than a Davison chart, synastry, coalescent chart, or other relational comparison tool. The 'Comparisons' group label is only a broad hint and does not provide selection criteria.

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