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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), so the description is free to add real behavioral detail: it discloses edge-case handling for lunar and leap-month dates, solar-term month boundaries, and local solar-time correction, plus a data-handling guarantee ('the input is not stored') that no annotation conveys. It stops short of describing failure behavior for invalid dates or out-of-range coordinates.

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?

Three sentences, front-loaded with the verb and resource, then outputs, then input-format edge cases, then the storage disclaimer. The output enumeration is long but earns its place because no output schema exists; nothing is redundant with the title or schema.

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?

For a 10-parameter domain-specific tool with no output schema, the description carries the return-value burden well and covers the tricky calendar/locale cases. The remaining gap is conditional behavior: it does not say whether omitting gender or location silently suppresses the luck cycles or solar-time correction, which matters for correct invocation.

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 baseline would be 3, but the description adds meaning the schema does not: birth_place/latitude/longitude are explained as feeding local solar-time correction rather than being an unexplained locator, and the lunar/leap-month path ties calendar and lunar_leap_month together. That linkage is genuine semantic value beyond the per-field descriptions.

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?

Specific verb plus resource ('Calculate a Korean saju / Chinese BaZi chart from a birth date'), followed by an enumeration of exactly what the chart contains (pillars, day master, five-element counts, ten gods, luck cycles, solar terms). It also distinguishes itself from the fortune/interpretation siblings with 'Calculation only', so an agent can tell it apart 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?

'Calculation only; the input is not stored' establishes the context in which this tool is appropriate versus the interpretation-oriented siblings. It does not explicitly name an alternative for follow-up interpretation (e.g. point at the fortune tools), so the routing guidance is clear but not exhaustive.

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