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

Beyond the readOnly/idempotent annotations, it discloses that bots are excluded, no cookies or IPs are used, and that Free accounts lack breakdowns and are limited to 7 days. It doesn't need to explain returns since no output schema exists, but it could note rate limits or freshness. The added context is substantial.

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 three sentences with no wasted words, front-loading the primary metrics before plan-specific details. The list of breakdowns is dense but necessary for completeness, though it could be slightly tighter.

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 read-only stats tool with no output schema, the description fully covers what is returned, plan limitations, period options, and data-collection caveats. An agent has all it needs to call the tool correctly given the plan context.

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 coverage is 100%, so the parameter meanings are already fully documented. The description adds plan-based semantics for 'days' (Free accounts always get 7) and implies the site parameter is required by saying 'for one site', but it doesn't give format examples beyond the schema. Baseline 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?

The description opens with a specific verb and resource ('Returns traffic statistics for one site') and then enumerates the exact metrics. It is clearly distinguishable from siblings like list_sites or get_site, which deal with site metadata rather than traffic.

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?

It implies when to use the tool (to get traffic stats) and states plan-based constraints (Free accounts get only 7 days), but it does not explicitly name an alternative tool or say when not to use it. The context is clear, yet no exclusions are given.

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