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

No annotations provided, so description carries full burden of behavioral disclosure. While 'Gets' implies read-only access, the description omits critical behavioral context: the ranking/severity system (despite rankBy/direction parameters), pagination behavior, what constitutes 'performance metrics' (Web Vitals), and output format constraints.

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 single sentence is efficient without redundant phrasing, but is undersized for a tool with 13 parameters and complex filtering capabilities. The material is front-loaded (verb first), yet lacks supporting sentences warranted by the tool's complexity.

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?

Insufficient for a feature-rich tool with date ranges, pagination, statistical measures (P75, P90), device filtering, and severity ranking. Missing explanation of the 'severity' concept, the relationship between metric and ranking, and how results are aggregated.

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?

Input schema has 100% description coverage, meeting baseline expectations. The description adds no supplemental parameter guidance (e.g., date format conventions, metric abbreviations like INP/CLS), relying entirely on schema documentation.

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 specific action ('Gets') and scope ('performance metrics broken down by country'), identifying the geographic dimension. However, it does not explicitly differentiate from sibling tools like 'get_page_performance_breakdown' or 'get_page_performance_breakdown_by_browser'.

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?

Provides no guidance on when to use the country-specific breakdown versus other breakdown tools (e.g., by browser or aggregate), nor does it mention prerequisites like domain validation requirements.

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