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

Annotations already declare readOnlyHint=true, covering the safety profile. The description adds valuable behavioral context by detailing the output format and noting that the dimension value is an ISO alpha-2 code that drops into a country filter, but it does not mention edge cases or limitations.

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 a single sentence that efficiently conveys purpose and output structure, with the key information front-loaded and a concrete example. It is highly scannable with zero wasted words.

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 no output schema, the description compensates by fully specifying the return structure, including dimensions, labels, and metrics. Given the read-only annotation and complete parameter documentation, this is adequate for a simple top-list tool, though error handling and pagination are not addressed.

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 schema fully documents all three parameters with descriptions (100% coverage), so the baseline is 3. The description does not add significant parameter-specific meaning beyond the output format hint, which is marginal.

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 explicitly states 'Top countries by visitors for a site' and provides a detailed return structure with example output, clearly distinguishing it from sibling top_* tools by specifying the dimension (country). The verb and resource are 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 does not offer guidance on when to use this tool versus alternatives like top_pages or top_sources. It only describes what it does without mentioning conditions or exclusions, leaving the agent to infer usage context.

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