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

Annotations already cover the safety profile (readOnly, idempotent, closed-world), and the description goes well beyond them: it discloses that timezone/DST rules and longitude→true-solar-time conversion are applied, that the year rolls at Li Chun, and that the day changes at 23:00 true solar time. These are non-obvious domain conventions that materially affect interpreting the result.

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 sentences, zero filler, front-loaded with what is computed before the return-value summary. The parentheticals earn their place by pinning down the two most easily misread conventions.

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?

No output schema exists, yet the description enumerates the return contents (pillars, Day Master, five-element counts, time conversion details) and covers the edge cases an agent would otherwise guess at — DST, Li Chun year boundary, 23:00 day rollover. Complete enough to call correctly.

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, but the description adds real meaning: it explains why timezone and longitude matter (zone rules with DST, true solar time conversion). It does not restate the accepted datetime format, which the schema already handles.

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-and-resource pair: computes the Four Pillars (八字) for a birth moment. The domain specificity makes it clearly distinct from the sibling tools best_times, qimen_chart and solar_terms without needing to name them.

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 phrase 'for a birth moment' implies the intended use case, but there is no explicit guidance on when to choose this tool over qimen_chart or solar_terms, and no stated exclusions or prerequisites.

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