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 that lang parameter can return English fallback per field with no translation, and that compact returns lossless token savings — both are behavioral details beyond the schema that help an agent predict behavior. It does not it does not mention the possibility of invalid sign output, but that's a minor gap.

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 one substantial paragraph with high information density. It front-loads the core action, then the output fields, and the use cases at the end. Nothing is duplicative of the schema; every sentence adds something. It is somewhat lengthy, but comprehensively informative.

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?

The description is complete for a read-only retrieval tool: it lists all returned content categories, parameter handling, language behavior, fallback translation, compact mode, and typical use cases. Combined with the annotations (readOnlyHint) and the absence of an output schema, there's nothing important missing. Edge cases like invalid sign are not documented, but the description's rich detail exceeds the minimum.

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 description elaborates on the id parameter by giving examples ('aries', 'Aries', 'ARIES') and explains response content per language. The description also explains what compact does more clearly than the schema (lossless, 40-52% token savings). It therefore adds value on top of a fully self-documenting schema, so above baseline 3.

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 clearly states the tool retrieves comprehensive zodiac sign information for any astrological sign using lowercase ID or case-insensitive name. It enumerates the specific fields returned (element, modality, ruling planet, etc.), which distinguishes it from the sibling get_astrology_signs (likely a list) and the horoscope/moon-phase tools. The verb 'retrieve' signals a read operation.

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 does not explicitly name alternatives or exclusions, but it does say what the tool is for, listing use cases like horoscope readings, compatibility checks, and birth chart interpretations. Given the sibling list, any tool whose name contains 'sign_id' is clearly the singular-profile variant, while the others are daily/weekly/monthly horoscopes or power calculations. It could be stronger by explicitly saying 'not for daily horoscopes' but the context signals are enough.

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