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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so safety is covered; the description adds real method context (exact Start of Spring, solar months) and the facts-only contract. The notable gap is it does not disclose what happens when the optional birth_time or location is omitted — presumably the hour pillar cannot be computed, but that behavior is left implicit.

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?

One dense sentence carries the definition, method, and outputs, followed by a short query-matching line and a scoping clause. Every sentence earns its place and the most important information (what it computes) comes first.

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 compensates well by enumerating the returned components (four pillars, Day Master, five-phase count). What remains unaddressed is optional-input behavior — how the result degrades without birth_time or location — which matters for a deterministic astronomy-style calculation.

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 100%, so the format of every parameter is already documented and the baseline is 3. The description adds only the loose mapping 'birth date, time and place', which hints that city/timezone exist to establish place, but it does not clarify when birth_city should be used versus birth_timezone or how a missing place affects accuracy.

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 computation (deriving year/month/day/hour pillars, Day Master and five-phase count) from a specific input (birth date, time, place), and names the method (BaZi, 四柱, exact Start of Spring and solar months). It is clearly separable from siblings like get_chinese_zodiac or convert_lunar_date, which return different artifacts.

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 concrete trigger phrasing ('what is my BaZi', 'my four pillars', 'my day master', '我的八字') so the agent knows when to route here, and adds a scope boundary ('Facts only, no readings'). It never names an alternative sibling or states when another tool would be preferred, so it stops short of full when/when-not guidance.

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