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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false and openWorldHint=false, so the safety profile is fully covered by structured data. The description adds genuinely useful non-schema context — endpoint, required inputs, and a 10-credit Tier 1 cost — which helps an agent budget before calling. It says nothing about what the response contains, and 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?

The definition is short, front-loaded with the functional sentence, and the bracketed metadata block is easy to scan. Nothing is padded. The only weakness is that its brevity comes at the cost of substance rather than from tight editing of rich content.

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 15-parameter astronomical calculation with only 33% schema coverage, the description does not explain how the optional chart parameters interact (sidereal vs tropical, ayanamsa selection, timezone resolution rules) or what distinguishes the output. The presence of an output schema excuses it from describing return values, but the input complexity is left largely undocumented.

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 only 33% across 15 parameters, so the description is expected to compensate, yet it merely repeats the four required names that the schema already declares as 'required', adding zero semantic meaning. The numerous chart-shaping options (ayanamsa vs ayanamsaId, zodiacType, houseSystem, precision/fields compact mode, timezone vs timezoneOffset) receive no explanation or interaction guidance in the description.

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 states the resource ('days of week traditionally aligned with the sign'), and the '[Group: Pet Astrology]' tag clarifies the domain, so an agent can tell it is about lucky weekday identification for a pet. However, it never states a verb, never explains whose 'sign' is meant (presumably the pet's Sun sign derived from the birth data), and is close to a restatement of the title 'Lucky Days'. It does not distinguish the tool from sibling lucky-day tools such as astroway_financial_lucky_day or astroway_chinese_feng_shui_lucky_directions.

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?

There is no 'when to use' guidance, no exclusions, and no mention of the alternatives (astroway_pet_sun_sign_meaning, astroway_financial_lucky_day, the calendar/muhurat tools). The required-parameter and cost lines are operational facts, not usage guidance. An agent must infer the use case entirely from the tool name and group tag.

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