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

With no annotations, the description carries the full burden and does well: it discloses the computation method (Zhi Run, verified against a classical ledger), that results are deterministic, the full return payload shape, and that the call is free with no quota consumed. It omits only minor operational details, e.g. whether there are any input-validation constraints or latency considerations.

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 dense sentences with the core action front-loaded and the return payload and cost signal following. No wasted prose, though the parenthetical method citation sits slightly ahead of the more actionable output summary.

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 deterministic computation tool with no output schema and full schema coverage, the description covers purpose, outputs, cost, and language. The only real gap is guidance on choosing between this and bazi_chart for a given divination request.

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 all four parameters are already documented at source. The description restates language support ('中文/English via lang') but adds nothing about date format, scene semantics, or defaults beyond what the schema states — baseline 3.

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 verb+resource (cast a Qimen Dunjia chart for a date/time) and enumerates what the chart contains — 9 palaces, deities/stars/gates, void palaces, formations, and a rule-based reading. It does not differentiate itself from the sibling bazi_chart, so an agent cannot tell from the description alone which charting system to pick.

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?

'For a given date/time' implies the trigger (any dated divination request), but there is no explicit when-to-use / when-not guidance and no mention of when to prefer this over bazi_chart. The 'scene' parameter's role in shaping the reading is left implicit.

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