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

Annotations already declare readOnly/idempotent/non-destructive/closed-world, so the safety profile is covered. The description adds real domain behavior beyond the annotations: the sign is determined by the exact Lichun instant rather than a calendar-year cut, which materially affects results.

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?

Two sentences, front-loaded with the output and then the boundary-case instruction; nothing is wasted. The trailing group/cost tags are metadata rather than prose, so they don't hurt the core definition.

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?

An output schema exists, so return values need no explanation, and the tz/offset/precision params are documented in the schema itself. For an 8-parameter tool the description covers the output and the one genuinely tricky input case, leaving only minor gaps such as solarYear's purpose.

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 coverage is 50% and the description adds meaning for two of the undocumented-in-prose parameters (time and timezoneOffset) by tying them to the boundary-day case. It says nothing about date, solarYear, language, or why offset and timezone are mutually exclusive, so it only partly compensates for the coverage gap.

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?

It names a specific verb-less but concrete output: the Chinese zodiac animal sign of the birth year plus the full pillar (stem + branch + element), which is more than the name alone conveys. It distinguishes itself from other zodiac siblings by defining the Lichun boundary, though it doesn't explicitly contrast with astroway_chinese_zodiac_element or astroway_chinese_zodiac_inner_animal.

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?

It gives one concrete conditional (pass time + timezoneOffset for births on the boundary day), which is genuine when-to-use guidance for an edge case. However, it never states when to prefer this tool over the many neighbouring zodiac/bazi pillar tools, so routing is left to inference.

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