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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the safe read-only nature of the operation is conveyed. The description adds no behavioral detail beyond the basic grouping operation, such as response shape, pagination behavior, or auth requirements. It is consistent with annotations and adds marginal context, so a 3 is appropriate.

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, front-loaded sentence with no filler. It communicates the core purpose efficiently without repeating the tool name or restating schema details.

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?

The tool has a rich input schema covering all parameters and an output schema, so the description does not need to explain return values or parameter formats. The main missing piece is usage context relative to sibling tools, but given the strong schema and annotation coverage, the description is largely complete for a read-only breakdown endpoint.

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 input schema has 100% description coverage for all 27 parameters, so the schema already documents each parameter thoroughly. The description contributes no additional parameter-level meaning. With full schema coverage, the baseline of 3 applies.

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 states a specific verb and resource: 'Get visitor breakdown by city.' It is clear that this tool returns per-city visitor data, and the city resource distinguishes it from sibling tools like get_countries and get_regions. However, it does not explicitly differentiate itself from those siblings, so it stops short of a 5.

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 provides no guidance on when to use this tool versus alternatives such as get_breakdown, get_regions, or get_countries. There is no mention of which scenario calls for city-level breakdowns or when another breakdown tool would be more appropriate.

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