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

No annotations exist, so the description carries the burden and does add real behavior: it discloses the Lunar New Year and Start of Spring boundary handling and enumerates the forecast sections returned, which substitutes for the missing output schema. It does not mention behavior for invalid/implausible years or whether the forecast is fixed to 2027 only.

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?

A single well-formed sentence that front-loads the primary lookup and then the returned forecast. No filler, no repetition of the title.

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 no output schema, the description usefully summarizes the return payload (love, career, money, tip) and the boundary-handling nuance that affects accuracy. Minor gaps remain around error behavior and whether non-2027 years still produce a sign-only result.

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%, so birth_date, timezone and language are already fully documented, including the Jan–Feb exactness caveat. The description reinforces but adds no syntax or format detail beyond the schema, so baseline 3 applies.

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?

States a specific verb and resource ('Find a person's Chinese zodiac animal from a birth year or date') plus the second output ('2027 Year of the Fire Goat forecast'). Sibling tools (bazi_chart, tarot, I Ching) are clearly different domains, so an agent can pick this without opening the schema.

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 makes the trigger condition clear: birthday/year in, sign plus 2027 forecast out, with a full date required for January–February exactness. It gives no explicit exclusions or naming of alternatives (e.g. bazi_chart for a deeper chart), so it stops short of full routing guidance.

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