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

With no annotations, the description must carry the behavioral burden, and it does add the meaningful detail that distance is spherical great-circle (haversine) rather than ellipsoidal, plus the selectable output units. However it says nothing about being a pure/side-effect-free computation or the precision implications of the model, so it is partial at best.

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 tight sentences, zero waste, with the core operation and return units both front-loaded. Nothing could be trimmed without losing information.

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 pure-computation tool with no annotations and no output schema, the description conveys the operation, the algorithm, and the return units, so essentially everything needed to invoke it is present. The only minor gap is not stating the output shape (scalar number vs object).

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 0%, but the nested payload's lat/lon fields are self-documenting by name and range. The description does add value by enumerating the available unit outputs (km, mi, nm), matching the schema's unit pattern, but it adds no lat/lon format or ordering guidance beyond that.

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?

Names a specific verb and resource: computing great-circle distance between two lat/lon points, and identifies the algorithm (haversine). This clearly separates it from sibling geo tools like geo_bearing and geo_midpoint, though it never names those alternatives explicitly.

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 only implied by the tool's function — an agent can infer it is for measuring point-to-point distance, but there is no statement of when to prefer it over geo_bearing, geo_midpoint, or geo_bbox, and no prerequisites or exclusions are given.

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