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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false, and openWorldHint=false, so the safety profile and determinism are handled. Beyond that the description adds real context the annotations don't cover: the computation basis is Korea time, content is published daily by sazuai.com (a freshness/source signal), and the full set of returned fields is disclosed despite there being no output schema.

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, front-loaded with the operation and its scope, then input formats, then source. The parenthetical field list earns its place since no output schema exists. Minor redundancy in restating the Korean/English animal input, which the schema already covers.

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 three-parameter read-only tool with no output schema, the description covers purpose, time zone, accepted input forms, source, and returned fields — enough to call it correctly on the first attempt. Gaps are minor: no statement on what happens with an invalid animal name or an out-of-range birth year, and no note on the default answer language.

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 67%, so the schema already documents animal and lang. The description reinforces the accepted animal forms and, importantly, gives the day parameter semantic footing ('today's or tomorrow's fortune (Korea time)'), which the day enum itself doesn't explain. However, it never mentions the lang parameter's effect on the answer language, which is the one under-documented dimension.

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 verb and resource — a daily fortune for one of the 12 zodiac animals (띠), covering today or tomorrow in Korea time — and enumerates exactly what comes back (luck score, love, money, health, advice, lucky color/number). The daily scope implicitly contrasts with the sibling get_2027_zodiac_fortune, but no sibling is named outright, so differentiation is left for the agent to infer.

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 makes the use case obvious (fetch one animal's fortune for today or tomorrow) but offers no explicit when-to-use or when-not-to-use guidance, nor does it route the agent toward calculate_saju or get_2027_zodiac_fortune for other time horizons. Usage is inferable, not stated.

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