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

There are no annotations, so the description carries the full burden of behavioral disclosure. It does disclose meaningful output behavior, such as the complete ZIP-code list for US cities with coordinates, time zone, and area codes. However, it does not mention whether the operation is read-only, what the response shape looks like, or any error/availability considerations.

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 front-loaded with the core subject and content, then moves to parameter sourcing. It is reasonably concise, though the first sentence is dense and 'ZIP codes' appears twice, creating mild redundancy without padding.

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 key facts an agent needs: what the group represents, what data is included, and where to get the required slugs. It is not exhaustive—country semantics and response shape are missing—but it is sufficient for correct invocation in most cases.

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 0%, so the description must compensate. It explains that region and group are slugs sourced from get_region or record fields, which adds real meaning beyond the bare schema. However, the country parameter's format and accepted values are not explicitly described, leaving the compensation incomplete.

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 clearly identifies the resource as a city/département/province/post office/delegation and states what it contains: all localities/ZIP codes. It differentiates the tool from siblings like get_region and lookup_postal_code by describing the group-level output. It lacks an explicit verb such as 'returns', but the intent is unambiguous.

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 gives clear invocation context by stating that region and group slugs are required and where to obtain them ('both from get_region or from any record's region.slug / group.slug'). It does not explicitly state when not to use this tool or name alternative sibling tools, 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.