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 is covered and the bar is lower. The description adds useful scope beyond that: it enumerates the breadth of the response (all twelve compatibility verdicts, strongest matches named), which tells the agent this is a comprehensive single-call lookup rather than a narrow field fetch.

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?

A single front-loaded sentence that leads with the verb and resource, then enumerates the payload. The field list is long but each item earns its place by signalling available data; there is no filler or repetition.

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?

An output schema exists, so return-value detail is not required, and annotations cover the safety profile. What remains useful — the kind of content returned and its comprehensiveness — is present, making this adequate for a simple single-parameter lookup.

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?

There is one parameter with 100% schema description coverage, and the schema already documents the example format and case-insensitivity ('such as Taurus or Aquarius, in any letter case'). The description only refers to 'a zodiac sign' generically and adds no constraint or format meaning beyond the schema, so baseline 3 applies.

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 opens with a specific verb ('Returns') and resource ('a zodiac sign's dates, element, modality, ruler and polarity, its traits...'), so the agent knows exactly what data this tool yields. It does not differentiate itself from siblings like check_sign_compatibility or get_birth_chart, even though the 'compatibility verdict with all twelve signs' overlaps with the former, leaving the agent to infer the distinction from names alone.

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?

Usage is only implied by the payload enumeration: call this when you need a full profile for a single named sign. There is no explicit when-to-use statement, no exclusion, and no pointer to check_sign_compatibility for pairwise questions or to find_sun_sign for locating a sign in the first place.

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