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

Annotations already establish readOnly, idempotent and closed-world behavior, so the safety profile is covered. The description adds genuinely useful non-obvious context: the fixed category set and the 'Unknown' caveat for visits predating tracking, which prevents misreading the data.

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 short sentences, front-loaded with the core purpose, then the data-quality caveat. Every clause earns its place with no redundancy.

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 simple read-only breakdown with no output schema, the description covers what is returned (the category list) and the key data caveat. With 100% schema coverage on inputs, nothing material is missing, though it does not mention result sizing or ordering ties.

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?

Schema description coverage is 100%, with limit, range and domain all documented in the schema (including defaults and the 90d cap). The description adds nothing about parameters, so the baseline of 3 is appropriate.

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 verb-and-dimension ('ranked by pageviews') on a specific resource (operating systems), and enumerates the categories returned. It is immediately distinguishable from sibling breakdowns like top_browsers, top_countries and top_pages.

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 implied by the name and the enumerated categories, but there is no explicit statement of when to pick this over top_browsers/top_countries or any prerequisite (e.g. auth/site scope). The agent can infer the context but is not guided.

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