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

Annotations already declare readOnlyHint, idempotentHint, and openWorldHint=false, so the safety profile is covered. The description adds useful behavioral context beyond annotations: supported date range, tropical zodiac frame, returned speed/retrograde data, and the proleptic Gregorian rule before 1582.

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 two compact sentences with no wasted text. The core purpose is front-loaded, followed by the date range and calendar caveat.

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 single-body lookup with three parameters and no output schema, the description covers the main scope, return content, date range, and calendar behavior. The remaining gap is that body enum semantics and more precise input expectations are left to the 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?

Schema description coverage is only 33%, so the description must compensate. It adds meaningful semantics for the date parameter, including the supported range and calendar handling, but it does not explain the body choices or add detail beyond the date pattern and time_utc default already in the schema.

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 resource and scope: one body's tropical position on a date, including speed and retrograde status. It is clear enough to distinguish from generic sky/chart tools, but it does not explicitly name or contrast with siblings such as sky_now or transits.

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 'For historical and ancient dates' gives an implied usage context, and the date range clarifies applicability. However, it does not explicitly say when to use this versus alternatives like sky_now or natal_chart, nor does it state exclusions.

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