Yearly Hexagram

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

Annotations already declare this a read-only, idempotent, non-destructive computation, so the safety profile is covered. The description adds genuinely non-obvious context: the formula is a documented deviation from standard Mei Hua practice, explicitly labelled `basis: convention`, and it states the return includes the full Legge reading and ti/yong. The credit cost and endpoint are also disclosed.

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?

The purpose and the method caveat come first, followed by the return contents and a compact bracketed block for group, endpoint, required fields and cost. Every sentence carries information and nothing is repeated from the 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?

With an output schema present, return values need not be explained, yet the description still signals the Legge reading and ti/yong. Required inputs, cost tier and the non-standard-formula caveat are all disclosed, so an agent has everything needed to call this correctly and interpret the result honestly.

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 75%, so the schema does much of the work, but the description adds real meaning: the year is consumed by its earthly branch, and birth date/time supply the lunar month, day and hour terms of the cast. Only timezoneOffset goes unaddressed in the description, which keeps this short of a 5.

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 names a specific resource (a yearly hexagram for a person) and specifies the derivation method: the Mei Hua formula using the year's earthly branch in place of the question-time year. It implicitly separates itself from question-based casting siblings by noting 'Mei Hua casts for a question, and this annual use is this API's convention,' though it does not name the alternative tools directly.

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 establishes the usage context clearly: an annual reading for a specific person and year rather than a question-driven cast. It does not explicitly say when to prefer a sibling such as a by-question or plum-blossom tool, but the contrast with question casting gives an agent enough to route correctly.

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