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

Annotations already mark the tool as read-only, but the description adds valuable context: 'Nothing is stored' addresses privacy, and 'Says so explicitly when Venus changed sign that day and the hour decides' discloses a key edge-case behavior. No contradiction with 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?

Three tightly written sentences: the first states the core function, the second notes the minimal input, and the third covers edge-case behavior and privacy. No filler or redundancy.

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 simple read-only tool with full schema coverage and annotations, the description covers the critical edge case (sign changes) and reassures about data storage. The sibling tools clearly position it outside the tarot category, so the description is sufficiently complete.

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 100% with both 'date' and 'language' parameters documented. The description reinforces the importance of the date parameter but does not add meaning beyond the schema. 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 a specific verb ('Compute') with a clear resource ('which zodiac sign Venus stood in on a given date') and distinguishes the tool from Sun sign readings. This also differentiates it from the tarot-related sibling tools, making its purpose unmistakable.

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 phrase 'Needs only a date' gives clear context for when to use the tool, and 'as distinct from their Sun sign' helps disambiguate its scope. However, it does not explicitly name alternative tools or state when not to use it, so it falls just short of a 5.

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