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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false, so the safety profile is covered. The description adds valuable behavioral context: the 23:00-00:00 slot is returned separately as lateZi, the hour pillar turns at 23:00 while the day pillar does not, and the tool returns element counts for the whole chart at each hour. It also notes the HTTP endpoint, which is extra transparency.

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 compact and front-loaded with the core purpose, then explains the lateZi edge case and the distinction from Western hours. The HTTP endpoint sentence is slightly redundant but not wasteful. Every sentence earns its place.

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, idempotent tool with 100% schema coverage and no output schema, the description covers the key behavioral nuance (lateZi) and the scope of results. It doesn't describe the return format in detail, but with no output schema and a clear description of what is returned, this is adequate.

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 description coverage is 100%, so the schema already documents all four parameters. The description adds context about the date being a local civil date and the element parameter ranking hours, but doesn't add much beyond the schema. 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?

The description clearly states the tool returns the twelve Chinese double-hours of a civil date, with hour pillar, hidden stems, ten god, and element counts. It explicitly distinguishes from Western planetary hours and mentions the lateZi edge case, making it distinct from siblings like asternym_bazi.

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 the lateZi/earlyZi distinction and clarifies these are Chinese double-hours, not Western planetary hours. It doesn't explicitly name sibling alternatives or state when to use this vs asternym_bazi, but the context is clear enough for an agent to select it for hour-level BaZi data.

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