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

With readOnlyHint, idempotentHint, and destructiveHint annotations already covering the safety profile, the description adds meaningful behavioral context: the year boundary is Li Chun, a missing time produces no hour pillar and the response explicitly says so, and no noon substitution is made. Nothing contradicts the annotations.

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?

Four sentences, with the return payload front-loaded before the important behavioral caveats. Only the 'same thing over HTTP: POST ...' sentence is arguably redundant, but it is short and does not obscure the needed 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?

For a complex divination tool with no output schema, the description enumerates all major returned data and flags two decisive input edge cases: Li Chun and missing time. It does not specify response formatting, errors, or rate limits, but the annotation-safety profile plus schema cover most operational gaps.

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?

The schema already documents all five parameters at 100% coverage, so the baseline is 3; the description adds value by explaining the date-boundary rule that affects 'date' interpretation and the no-hour-pillar behavior that depends on 'time'. It does not describe 'tz' or 'agent', but the schema covers those adequately.

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 enumerates a specific output set—pillars, day master, hidden stems with ten gods, element counts, dominant/missing elements, na yin, twelve stages, and void branches—so an agent knows exactly what this tool produces. The title's 'Four Pillars alone' plus the sibling list distinguishes it from asternym_bazi_hours, numerology, reading, and zodiac.

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 implies use when a BaZi Four Pillars chart is needed and clarifies edge cases such as missing time and the Li Chun year boundary, but it never names an alternative or states when not to use this tool versus asternym_bazi_hours or other siblings. Usage guidance is inferred from the title and content, not explicit.

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