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

Annotations only cover the safety profile (readOnly, idempotent, non-destructive, open world); the description adds genuinely new behavior: a first-request OSM fetch followed by cache serving, a 1-unit cost, and a keyless tier for low detail. It also discloses the failure mode where oversized polygons return geometry=null with a download_url, which 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?

Four dense sentences, front-loaded with the return shape before cost, tiering and truncation caveats. Every clause carries information an agent would otherwise have to discover by trial.

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?

There is no output schema, and the description compensates by describing the returned Feature, listing the property keys, and explaining the null-geometry plus download_url fallback. For a single-resource read with trivial side effects, nothing needed for a correct call 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 meaning beyond the schema by tying detail to key tier ('detail=low is also public without a key') and clarifying that include=parents pulls the full hierarchy while children gives direct subdivisions only. Coordinate precision and id format are left entirely to the schema.

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 ('Returns one boundary as a GeoJSON Feature') and immediately enumerates the payload: polygon plus named properties. The singular 'one boundary' also distinguishes it from search_boundaries and list_children without opening their schemas.

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?

Gives concrete operational context: costs 1 unit, detail=low works without a key for map previews, and include=parents/children selectable extras. It does not name an alternative tool or an explicit when-not-to-use condition (e.g. vs search_boundaries when the id is unknown), so it stops short of a 5.

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