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

Annotations already declare readOnlyHint and idempotentHint, so the description's added value is the failure contract: invalid time or gender returns an error and the tool will not guess the birth hour. It also constrains input provenance to user-confirmed facts or subject_candidates, which is real behavioral context beyond the annotations. Return values are left to the output schema, which exists.

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?

Front-loaded with the operation, then provenance, then error behavior, then routing to the sibling. Dense but every clause carries information; the only mild cost is that several constraints are packed into single sentences.

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?

Covers purpose, input provenance, error behavior, and sibling routing, while annotations carry the safety profile and an output schema exists to explain returns. Nothing an agent needs in order to call this correctly is missing.

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% and the nested subject object is documented, so the baseline is 3. The description adds meaning the schema cannot express: the subject must originate from confirmed facts or subject_candidates, and standard_time is used for the 立春 year boundary, clarifying why the field matters.

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?

Names a specific verb and resource set: derives birth year and gender from a calibrated subject, then computes 命卦, 四吉四凶方, and 出生年紫白飞星. It explicitly separates itself from bazhai_layout (门/主/灶), so an agent can distinguish the two without opening either 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?

States the triggering question class (住宅风水评估、命卦方位吉凶) and names the alternative for the door/main-stove case (bazhai_layout). It also adds a negative rule — 八宅不与八字四柱合参 — which prevents a plausible misuse with the bazi siblings.

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