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

Annotations already declare readOnly, idempotent, non-destructive, and open-world, so the safety profile is covered. The description adds genuinely new behavioral context — 'Keyless', i.e. no authentication required — which an agent needs before calling. Return volume/pagination is not addressed, but that is a minor gap for a small enumeration endpoint.

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 sentences, front-loaded with the resource being listed and ending with the actionable routing rule. The em-dash clause ('with the description of what each covers') is slightly wordy but does convey what the listing returns, so it 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 zero-parameter, no-output-schema enumeration tool, the description covers purpose, return content (datasets plus coverage descriptions), auth posture, and positioning relative to the compute sibling. Nothing an agent needs in order 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?

The tool takes zero parameters, so the schema baseline is 4 and there is no parameter semantics for the description to add or omit. No documentation gap exists here.

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?

Specific verb (List) plus specific resource (WorldPop datasets/population surfaces exposed by the stats API), and it clarifies the scope of what can be summed over a polygon. It is immediately distinguishable from sibling worldpop_stats_polygon, which computes over a polygon rather than enumerating available surfaces.

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 an explicit routing rule: call this before worldpop_stats_polygon when you need something other than total population. The named alternative plus the selecting condition covers both when-to-use and the implicit when-not (total population only).

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