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

Annotations already cover read-only/idempotent/non-destructive, so the bar is low, and the description adds genuinely useful domain behavior: the 60-jiazi anchor (1990-01-01 = Bing-Yin), the 23:00 local rollover for day/hour, and the exact Lichun/節 instants for year/month. The 10-credit cost is also disclosed. It does not mention timezone requirements or output shape, but annotations plus the output schema carry those.

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?

Two tightly written sentences front-load the resource and the key computational rules, followed by compact group/cost metadata. No filler; each clause carries information.

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?

With an output schema present, return values need no explanation, and annotations cover the safety profile. The description supplies the timing rules an agent needs to interpret results correctly; the only gap is that it doesn't note the date/timezone prerequisites for accurate hour-pillar output.

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 57%: timezone, fields, precision and timezoneOffset are documented in the schema, while date and language are bare. The description only adds semantics for `time` (hour-pillar computation), so it does not compensate for the undocumented parameters. 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 names a specific resource (all four pillars: year, month, day, hour) and implicitly differentiates from the single-pillar siblings (bazi_year_pillar, bazi_month_pillar, bazi_hour_pillar) by emphasizing 'All four.' It is clear what gets computed, though it never explicitly names an alternative tool to route against.

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?

'Pass `time` to compute the hour pillar' is a usage hint for one parameter, but there is no explicit when-to-use/when-not guidance versus bazi_chart or the per-pillar siblings. The agent must infer that this is the full-chart option from the word 'All.'

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