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

Beyond the readOnly/destructive annotations it discloses pricing ($0.01/call via x402, first 25 free, failed calls free) and explains why idempotentHint=false in practical terms: each call is charged, so repeats are not free. It also flags a real correctness caveat (January/early-February dates may belong to the previous Chinese animal) that an agent could not infer from 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?

Front-loaded with what is returned, then the boundary caveat, then use cases, then pricing. Dense and mostly purposeful, though the pricing sentence runs long and could be trimmed without losing meaning.

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 no output schema, the description does name the returned components (sign, element, Chinese animal, Chinese element) and the edge-case flag, which covers what an agent needs to decide and call. It stops short of describing the response structure or field names, which would matter given the absent output schema.

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% and already documents the single parameter as YYYY-MM-DD, so the baseline is 3. The inline example (date=1990-08-15) reinforces the format and confirms a full-date string is expected, adding modest value beyond the schema.

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 resource and computation: the western (tropical) sign with element plus the Chinese animal and element for a birth date. It is clearly distinguishable from adjacent siblings such as date_info, calc_age, or holidays without opening any schema.

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?

"Use for profile enrichment, greeting cards, games or horoscope-style content" gives concrete usage contexts, and the example date anchors the expected input. It never names an alternative tool or an explicit when-not condition, so routing against siblings like date_info is left implicit.

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