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

Annotations already declare readOnly, idempotent and non-destructive, so the safety profile is covered. The description adds genuinely useful non-annotation context: the endpoint, the cost (50 credits, Tier 3), and the required inputs — the credit cost in particular informs an agent's decision to call this over a cheaper sibling.

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 purpose sentence is front-loaded and waste-free, and the bracketed metadata (group, endpoint, required, cost) is compact and scannable. Slightly mechanical, but nothing extraneous.

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 the cost, endpoint and required inputs are covered. It is nearly complete for a read-only generation tool; the main omission is whether only zodiac signs are needed (no birth data) and the default language behavior.

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 33% (6 params, mostly undocumented enums), so the description needs to compensate and does not. It only restates 'Required: sign1, sign2', which is already in the schema, and adds nothing about language defaults, disclaimer_inline behavior, or how sign1/sign2 ordering affects the synastry reading.

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 (Generate), a precise resource (relationship horoscope based on synastry between two charts), and enumerates the output substance (strengths, friction points, themes for the next 30 days). This clearly separates it from the single-sign siblings horoscope_daily/weekly/monthly/yearly and from the visual render_composite/bi_wheel tools.

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?

Usage is implied by the name and the phrase 'between two charts', so an agent can infer this is the compatibility/relationship tool. However, there is no explicit when-to-use versus when-not, no statement of prerequisites, and no named alternative (e.g., render_composite for a visual, ai_comparison_coach for narrative).

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