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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the description is not required to restate safety. It does add non-obvious context beyond them: regions may overlap, and the IDs are not distance or service-area boundaries — a caveat that prevents an agent from mistreating the returned data as geofencing.

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, both earning their place: the first states the returned content, the second carries the single important caveat. Front-loaded with no filler or restatement of the title.

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 zero parameters, full annotations and an output schema, the description covers what an agent needs to call it and to interpret the result. The one remaining gap is that it never connects the returned region IDs to the downstream tools that consume them.

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 no parameters, so there is nothing for the description to disambiguate. Baseline 4 applies; the description correctly spends no words on an empty input 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?

Description gives a specific verb and resource ('List supported region IDs') and names what the payload contains ('their included city/state addresses'), so an agent knows exactly what comes back. No sibling collision exists: the other tools are provider-centric, and none is a region lookup.

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?

Usage is only implied by the zero-argument, read-only shape of a lookup tool; the description never says when to call it or what to do with the IDs (e.g., pass them as filters to search_providers). The overlap caveat is interpretive guidance about the results, not when-to-use guidance.

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