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

With no annotations provided, the description carries the full burden for behavioral disclosure. It clearly states the output is ordered by distance, includes distance_km, and adds a non-obvious caveat that distances are to the locality centroid, not the boundary. This is valuable context beyond the schema.

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?

The description is two sentences that front-load the core action and output, then provide examples and a crucial caveat. There is no redundancy or filler; every sentence earns its place.

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?

For a tool with no output schema and no annotations, the description covers the input coordinates, output field, ordering, and an important distance caveat. It does not explicitly state default parameters, but the schema covers limit and radius_km defaults, and it does not describe no-result behavior, but overall it is sufficiently complete for correct invocation.

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 description coverage is 60%, with lat and lon lacking descriptions. The description clarifies that lat/lon define the center point and that the search radius in the examples maps to radius_km. It also explains the significance of the first result, adding meaning beyond the raw parameter definitions.

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 states a specific verb ('List'), a clear resource ('localities around a latitude/longitude'), and the output field ('distance_km'), with an ordering constraint ('nearest first'). The example use cases make it easy to distinguish this from siblings like search_places or lookup_postal_code.

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 explicitly names when to use the tool ('what ZIP codes are near…', 'postal codes within 10 km of…', 'resolve coordinates to the closest postal code'). It does not explicitly mention when not to use it or alternative tools, but the context is clear enough to guide an agent's selection.

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