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

The readOnlyHint annotation already signals a safe read operation. The description adds a concrete response shape example showing dimensions and metrics, including bounce_rate, which goes beyond the annotation and gives the agent a clear expectation of the return format. No side effects or destructive behaviors are relevant here.

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 compact: one sentence defining purpose plus a short, illustrative JSON output example. Every part serves a purpose, and the example is valuable because there is no output schema. It is not overly verbose.

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 query tool, the definition is complete: parameters are fully documented in the schema, annotations communicate safety, and the description supplies the missing return shape through an example. It could additionally mention default ordering or that results are sorted by visitors descending, but this is reasonably implied by the word 'top.'

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 already provides 100% coverage of all three parameters with detailed explanations for site, limit, and period. The description does not add additional parameter-level meaning beyond the schema, so 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 clearly identifies the tool as returning top traffic sources ranked by visitors for a site. It states the key resource ('traffic sources') and the metric ('by visitors'), making the tool's intent understandable. It does not explicitly differentiate itself from sibling tools like top_countries or top_pages, but the resource name is sufficiently specific.

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 implies the tool is for site-level traffic source analysis, and the context is clear. However, it provides no explicit guidance on when to choose this tool over top_countries, top_pages, or other top_* siblings. The usage context is implied by the name and description rather than stated as a rule.

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