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

With no annotations, the description carries the full behavioral disclosure burden and does well: it states the 1–9 range, that periods switch at Lichun rather than January 1, and that 1984 is anchored as the start of Period 7. It does not clarify the default date when the optional parameter is omitted, which is a minor remaining gap for a read-only calculation tool.

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 description is a single dense, front-loaded sentence that states the purpose and then the critical switching rule. Every clause earns its place, with no redundant restatement of the tool name.

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 simple single-parameter lookup with no output schema, the description is nearly complete: it defines the output range and the calendar rule governing period changes. The missing piece is date-parameter semantics, especially the default behavior, which matters because the only parameter is optional.

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?

There is one optional date parameter with 0% schema description coverage, so the description must compensate and does not. It mentions 'for a date' but provides no format, timezone, accepted range, or default behavior when date is omitted.

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 clearly identifies the resource as the San Yuan period (三元九运) and constrains the output to 1–9 for a given date. It is specific enough to distinguish this from sibling tools like calendar or ganzhi, though it does not use an explicit verb such as 'returns' or 'calculates'.

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?

Usage is implied by the niche concept: an agent can infer this tool is used when a San Yuan period is needed for a date. However, the description gives no explicit when-to-use guidance, no exclusions, and no alternatives among sibling tools such as solar_terms or flying_star_chart.

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