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

Annotations already mark the tool as read-only and non-destructive. The description adds useful behavioral context beyond that: the table is fixed for a building's lifetime, and the Period 9 vs Period 8 example clarifies how completion date affects the result. This is valuable but not exhaustive; no hidden destructive or state-changing behavior 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?

Three information-dense sentences that front-load the resource and scope, then explain the practical consequence with a concrete example. No wasted words, and the example earns its place by illustrating the edge case of a Period 8 building after Period 9 opens.

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 tool with zero required parameters and a fully documented schema, the description gives enough context to invoke it correctly. It explains the output's real-world meaning and field types, though it does not describe the exact JSON response shape. Since there is no output schema, a brief note on the response structure would push this to 5.

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 the baseline is 3. The description adds meaning to the 'date' parameter by linking it to building completion and current period, and it reinforces the lang/compact defaults are not needed for most calls. It does not substantially extend the schema's parameter documentation.

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?

States a specific resource—the nine 20-year periods of the San Yuan cycle—with a clear scope (1864 to 2043) and the exact data returned (ruling star, five phase, palace, Li Chun date, current period). The use case for natal chart determination further distinguishes it from sibling Feng Shui period-specific tools.

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 explains when to use this tool: to determine which period a building was completed in and therefore which natal chart applies. It does not explicitly name sibling alternatives or exclusion conditions, but the practical context is clear enough for an agent.

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