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

Annotations already establish readOnlyHint=true, destructiveHint=false, and openWorldHint=true, so the safety profile is covered. The description adds genuinely useful behavior beyond that: the exact GET endpoint and, importantly, a cost caveat noting that the docs do not clarify whether these helper lists are billed (though they are not searches). That billing note is real context an agent would not otherwise have.

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 clauses, front-loaded with the purpose and the parameter linkage before the endpoint and cost note. Tight and waste-free, though the opening fragment is slightly telegraphic.

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 trivial no-parameter, no-output-schema list endpoint, the description supplies purpose, the underlying route, and a billing caveat, which is nearly everything an agent needs. Nothing essential is missing, though the return shape is left implicit.

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 baseline is 4. The description still earns that level by connecting the returned values to the search_engine parameter consumed elsewhere, giving the output meaning relative to the rest of the API.

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 resource (search engine hosts Zenserp supports) and explicitly ties it to its downstream use (values for search_engine). This distinguishes it from sibling list tools like list_countries and list_languages, which enumerate different domains. It stops just short of 5 because the phrasing is a sentence fragment rather than a clean verb+resource statement.

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 parenthetical '(values for search_engine)' implicitly tells the agent this is the endpoint to consult before setting the search_engine parameter, which is useful guidance. However, there is no explicit when-to-use or when-not-to-use framing, and no mention of alternatives.

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