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

Annotations already cover read-only, idempotent and closed-world behavior, but the description adds genuinely new behavioral facts: a paid x402/USDC-on-Base billing model at $0.05 per successful call, and the important distinction that containment is planar while area/length are geodesic on WGS-84. Hole handling and the Feature-wrapping input form are also disclosed. It stops short of describing response shape or error behavior.

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, front-loaded with the capability list before the billing note, with no filler. It is slightly run-on packed, but every clause carries operational content.

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 read-only/idempotent annotations and no output schema, the description carries the return-shape burden and largely does so by enumerating the six computed values, plus input-type and geodesic/planar semantics. It is close to complete for a 4-parameter, single-purpose geometry tool.

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 baseline is 3, but the description adds meaning the schema lacks: area is 'signed' and expressed in square metres, length is geodesic, and containment handling is planar with hole handling on the geometry. Those unit and semantic details are not present in the schema text.

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 names the exact operations performed (containment, bbox, centroid, signed area, perimeter, winding) on a specific resource (a caller-supplied GeoJSON geometry), so an agent knows precisely what it does. It never names or contrasts against geo_distance/geo_geohash/geo_pluscode, so the sibling differentiation that would make this a 5 is absent.

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: the ops parameter and 'Default all' tell the agent what a call looks like, but there is no statement of when to prefer this tool over geo_distance or geo_pluscode, and no prerequisites or exclusions. An agent can infer the domain but is not routed.

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