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

Annotations already declare the read-only, non-destructive profile, and the description adds genuinely useful behavioral context beyond them: an auth requirement (subscription key) and the return format (GeoJSON). It omits rate limits or precision caveats, so it falls short of 5.

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?

Three short sentences, front-loaded with the core purpose and progressing to output format and prerequisite. No filler or repetition.

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 helpfully discloses the GeoJSON return type, covers the auth precondition, and the fully-described parameters leave little else needed. Minor gaps such as error behavior or band-ordering semantics keep it from 5.

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 lat, lon, costing, and contours are already fully documented in the schema. The description only restates the coordinate input and the four-band limit, adding no syntax or default details beyond the structured fields.

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 ('Calculate reachable-area polygons from a coordinate') plus the scope limit ('up to four travel-time bands'), which lets an agent distinguish it from the sibling route tool that returns paths rather than polygons.

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 clear use contexts ('catchment, coverage, and accessibility analysis') and a prerequisite ('Requires a subscription key'), but names no alternative tool or when-not-to-use condition.

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