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

Annotations already declare readOnlyHint, idempotentHint and non-destructive behavior, so safety is covered. The description adds the great-circle computation model, but omits the output unit (km/miles/nm), which is the main behavioral unknown for this tool.

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?

Two short, front-loaded sentences with the core action stated first. The second sentence is a lightweight bundle pointer that is arguably filler but costs little.

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?

An output schema exists, so return structure needn't be explained. However, distance units and the coordinate datum are left unspecified, which is a meaningful omission for a distance calculator despite otherwise adequate coverage.

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 each lat/lon clearly labeled departure/arrival and bounded by min/max. The description adds nothing beyond the schema, so 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+resource and even the method: 'great-circle distance between two coordinates.' That distinguishes it from a generic distance tool, though it does not name or differentiate from siblings such as calculate_distance_2d/3d or calculate_light_year_distance.

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?

'See list_bundles for related voyage calculators' is a cross-referral, not when-to-use guidance. It never says when to pick this over calculate_distance_2d/3d or what prerequisites apply, so an agent gets no routing help.

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