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

Annotations already declare readOnlyHint=true and destructiveHint=false. The description adds meaningful behavioral details beyond that: both cycles are returned as ordered rings and also attached to each phase, so a caller can render them directly without deriving. This explains the data shape in a non-obvious way.

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 with no filler: the first states what is returned, the second explains the cycle packaging, and the third gives the canonical-vocabulary context. Each sentence earns its place, though the title already conveys a similar top-line scope.

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 read-only list of five fixed phases with no required parameters, the description plus fully documented schema is sufficient. It explains the data contents, the cycle structure, and the canonical role. A response example or explicit return container would be nicebut is not necessary for such a constrained tool.

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?

Input schema coverage is 100%, with clear descriptions for lang, limit, offset, and compact, including enums, defaults, ranges, and fallback behavior. The description adds no parameter-specific semantics, so it does not need to compensate; baseline 3 is appropriate.

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?

Description states a clear action ('Return') and specific resource ('the five phases of Wu Xing') with exact attributes: Chinese character, season, direction, Heavenly Stems and Earthly Branches, and both cycles. It distinguishes itself from sibling zodiac/calendar/BaZi tools by positioning itself as the canonical five-phase vocabulary source.

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?

The description gives clear usage context: 'This is the one place the five phase vocabulary is defined' and names consumers such as BaZi charts, Na Yin, zodiac element variants, and feng shui stars. It does not explicitly state when not to use the tool or name alternatives, but no sibling element tool exists, so the context is strong.

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