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

Annotations already establish that this is a safe read-only operation, but the description adds substantial behavioral context beyond that: default full-history retention, cookieless-tracking effects on new_visitors and returning_visitors, a diagnostic rule for near-equal new_visitors and visitors, and the fact that visitors can exceed pageviews due to redirect hops. This is rich, actionable disclosure for interpreting results.

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 front-loaded with the metric list and then layers in important edge-case behavior. It is appropriately sized for the complexity, though the multi-sentence prose is slightly dense and could be tightened with bullet-like structure.

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?

There is no output schema, so the description should carry more of the return-value burden. It lists the headline metrics and critical caveats, but it does not describe the response shape or fully clarify date-range parameter interactions, leaving a minor gap.

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 75%, so most parameters are already documented in the schema. The description adds the default full-history behavior, but this is already implied by the days parameter description, and it does not clarify how from, to, and days interact beyond that default.

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 ("Headline KPIs for a site") and enumerates the metrics returned. It does not explicitly distinguish this tool from siblings such as get_breakdown or get_timeseries, so it is clear but not sibling-differentiating.

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 phrase "Headline KPIs for a site" and the default date-range note. However, the description gives no explicit when-to-use guidance or alternatives, so the agent must infer when to choose this over get_timeseries, get_breakdown, or get_visitors.

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