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

Annotations already provide readOnlyHint=true and destructiveHint=false, covering side-effect safety. The description adds useful context about scope ('tropical zodiac signs') and what data is included, but it does not disclose other behavioral traits like possible language fallback behavior or latency concerns. Given the safety profile is covered, this is adequate but not beyond what annotations already imply.

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 front-loaded with the core action ('Returns all 12 tropical zodiac signs'), follows with concise parameter-relevant info and use cases, and ends with the sibling alternative. The full list of suns is verbose but useful for agent recognition, and every sentence earns its place. No fluff.

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?

The tool has no output schema, so the description does a good job stating it returns the requested fields. It covers scope, signing list complete. The `lang` and `compact` behavior are only captured in the schema, but the description doesn't need to repeat schema-covered biases. It also clearly points to the detail endpoint for complete profiles. Missing only minor financial usage constraints, but those are well covered by annotations and 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?

The schema description coverage is 100%: both `lang` and `compact` have thorough descriptions in the schema, so the tool description adds no new parameter insight. It does not mention that `lang` or `compact` exist, but the schema fully covers their semantics, so a 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 states an exact action and resource: 'Returns all 12 tropical zodiac signs' and lists every one of them. It names the exact fields returned (name, symbol, element, date ranges, short descriptions), and explicitly distinguishes it from the sibling 'GET /signs/{id}' endpoint for detailed profiles. This leaves no ambiguity about the tool's role.

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 gives a range of concrete use cases ('zodiac sign lists, horoscope widgets, birth chart calculators, astrology app...') and explicitly says to use GET /signs/{id} when full profiles with personality traits are needed. This is a clear when to use/alternatives guidance, leaving no doubt about when this listing is preferred.

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