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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint=false and destructiveHint=false, so safety is covered. The description contributes the deterministic scoring canon and the 0-100 range, which is genuine added context, but says nothing about what the response contains, rate limits, or determinism caveats beyond idempotence.

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 core sentence is front-loaded and wastes no words; the bracketed metadata block is terse and scannable. Slightly redundant in that Required/Cost duplicate structured data, but the overall package is compact.

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?

With an output schema present, return values need not be described, and annotations cover the safety profile, so the essentials are present. However, for a 5-parameter tool with nested person objects and 40% schema coverage, the description leaves input construction and any guidance on interpreting the score to inference, making it only minimally adequate.

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 only 40% and the description adds almost nothing: it merely repeats that person1 and person2 are required (already in the schema's required array). It does not explain the nested person shape (date/time/timezone/timezoneOffset), nor the compact-mode 'fields' and 'precision' parameters, so the low-coverage gap is not compensated for.

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 states a specific verb+resource (compute a pair compatibility score on the 0-100 scale) and even names the underlying method (San He trine + Liu Chong canon). This distinguishes it from single-person siblings like astroway_chinese_zodiac_animal or astroway_chinese_zodiac_element, though it never names an alternative explicitly.

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 only usage signals are the metadata tags '[Required: person1, person2]' and '[Cost: 10 credits (Tier 1)]', which restate the schema's required array and pricing rather than telling the agent when to pick this over e.g. astroway_mayan_compatibility or a relational synastry score. No when-to-use or when-not-to-use guidance is given.

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