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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered. The description adds useful return-payload context (km, AU, light travel time, provenance), but does not discuss data-source behavior, rate limits, or error handling.

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 compact and front-loaded, with the core operation and output units stated first and a short example appended. There is no wasted language.

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?

With no output schema, the description usefully explains the return values and provenance. However, it leaves gaps around accepted from/to values and when to choose this tool over distance_series, so it is adequate but not fully 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 only 33%: date is documented in the schema, but from and to have no schema descriptions. The example clarifies that from and to are object names like 'earth' and 'mars', but it does not define accepted identifier formats or the full range of valid values.

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 clearly states it computes centre-to-centre distance between two objects at a date, with units and light travel time. It is specific, but does not explicitly distinguish itself from the sibling perigee_distance_series, which is implied only by the single-date framing.

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 implied by the example and the 'at a date' phrasing, but the description gives no explicit when-to-use guidance, exclusions, or alternatives such as perigee_distance_series for time-series distances.

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