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

The description discloses key behavioral details beyond the annotations: it reports cusps rather than resolving them by assuming noon, and it explicitly states the calendar boundary choice (Lunar New Year over Li Chun). Since annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, these added details about calculation behavior provide meaningful context not available in structured fields. No contradiction with 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?

The description is two sentences long plus a note about the HTTP endpoint. It is front-loaded with the core purpose, then adds the calendar clarification, and finally the alternative access method. Every sentence earns its place with no filler or redundancy.

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?

Despite the tool having 6 parameters (only 1 required) and no output schema, the description covers the essential operational details: what it returns, how cusps are handled, the calendar boundary choice, and an alternative HTTP access method. It provides enough for an agent to correctly invoke the tool without missing critical context. The complexity is moderate, and the description is complete.

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 parameters are already documented. The description does not add new meaning to parameters beyond what the schema provides (e.g., it mentions cusp handling but that is a global behavior, not param-specific). It does not elaborate on tz, lat, lng, time, or agent beyond schema definitions. 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 explicitly states the tool returns both the Western sun sign (from ecliptic longitude) and the Chinese animal with element and polarity. It uses specific terminology ('Sun's sign from its apparent ecliptic longitude', 'Chinese animal, element and polarity') and distinguishes from the BaZi tool by highlighting the calendar boundary difference (Lunar New Year vs Li Chun). This clearly differentiates it from siblings.

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 when to use this tool versus the BaZi tool by noting the calendar difference ('the Chinese year here turns at Lunar New Year, while the BaZi year pillar turns at Li Chun'). This gives context for selection, but it does not explicitly name the alternative or say 'use this when'. Still, the guidance is clear enough for an agent to infer the appropriate choice.

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