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

Annotations already declare readOnly/idempotent/openWorld=false, but the description adds real behavioral context beyond them: the Vincenty algorithm with haversine fallback, the units returned, and notably the $0.05 per-call x402/USDC payment requirement, which an agent must know before invoking.

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 dense sentences that front-load the core capability and append units and pricing. Efficient with no filler, though the first sentence packs several capabilities together.

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 states the units returned (metres, km, nm, miles) and enumerates all operations and the destination inputs. It stops short of mapping which params each op requires, but the 100%-covered schema fills that 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%, so the schema already documents all nine parameters, including enums for op and method. The description reinforces op semantics and mentions bearing/distance for destination, but adds no syntax or meaning beyond the schema, so the baseline 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 precise verbs and resources: geodesic distance, initial/final bearing, midpoint, destination point, and cumulative path length. It is clearly a coordinate-math tool, distinguishable from geo_geohash, geo_pluscode, and geo_polygon siblings.

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 description enumerates the four operations, which implicitly signals usage, but it gives no explicit when-to-use or when-not-to-use guidance and names no alternatives. Selection among siblings is left to inference.

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