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 and idempotency profile is fully covered structurally. The description's only added behavior is the return field list, which duplicates the output schema rather than revealing anything new (units, precision assumptions, edge cases).

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 core purpose is front-loaded in a single tight sentence, and the whole definition is two sentences. The trailing list_bundles cross-reference is mild noise that does not help an agent invoke this specific tool, keeping it just short of a 5.

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 one fully documented parameter, complete annotations, and an output schema present, the description supplies everything needed to call the tool correctly. The only shortfall is that the return-value enumeration is redundant with the output schema rather than filling a real gap.

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 coverage is 100% with a single parameter, and the schema already specifies 'Observer height above ground in metres' with exclusiveMinimum 0. The description only restates 'from a given height' and adds no syntax, unit, or range meaning beyond what the schema provides, so the 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?

States a specific verb and resource ('Calculate the distance to the horizon') plus the input domain ('from a given height'), which cleanly separates it from adjacent siblings like calculate_hyperfocal_distance, calculate_distance_2d, or calculate_star_magnitude_distance. An agent can identify the tool's function without opening the schema.

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?

There is no statement of when to use this tool versus alternatives, no prerequisites, and no exclusions. The 'See list_bundles for related astronomie-nature calculators' line is a discovery cross-reference, not invocation guidance, so usage must be inferred entirely from the name.

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