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

Annotations cover the safety profile (readOnly, idempotent, closed-world), and the description goes well beyond them: it discloses the pricing model ($0.05 per successful call over x402/USDC on Base), the geodesic-versus-planar distinction for area/length versus containment, correct hole handling, and the input size limits. Payment and coordinate-system behavior are exactly the kind of traits an agent cannot infer from structured fields.

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 purpose and then the output set, with pricing last. No filler, though the enumeration of six outputs in one sentence makes it slightly heavy to scan.

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 enumerates every returned value (bbox, centroid, area, perimeter, winding) and specifies units (square metres), so an agent knows what it gets back. Combined with the pricing and geometry-acceptance notes, nothing needed to call it correctly is missing.

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 real semantic value beyond the schema: it explains that area and perimeter are geodesic on WGS-84 while containment is planar in lon/lat, which resolves ambiguity the schema's 'comma-separated subset' text does not. The 'ops' semantics (default all) are stated in both places.

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 ('point in polygon check') and enumerates the full set of computed outputs: bbox, centroid, signed area, perimeter, winding order. It also names the accepted geometry types, so an agent can distinguish it from sibling geo_distance 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?

It describes what inputs are accepted (Polygon, MultiPolygon, or a Feature wrapping either) and implies the containment test runs when lat/lon are supplied, but it never states when to prefer this over related siblings such as geo_distance or when the containment op is inapplicable. Usage is implied from the input description rather than stated as guidance.

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