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

Annotations already establish readOnlyHint=true and openWorldHint=true, so safety and live-data behavior are covered structurally. The description adds non-obvious behavior: every metric is compared against the equivalent preceding period, and milestones are surfaced — traits an agent could not infer from the annotations.

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?

Front-loaded with the payload contents and closed with a short routing cue; the metric list is dense but earns its place because no output schema exists. Slightly long single sentence, but no filler.

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?

With no output schema, the description usefully enumerates the returned metrics, comparison basis, daily series and milestones, and annotations cover the safety profile, so an agent can call it correctly. It omits any note on data freshness, pagination, or response shape beyond the metric names.

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?

Both parameters are fully documented in the schema (100% coverage), including the days default/max and the property default behavior, so the schema carries the load. The description only alludes to "the period" without adding syntax, format, or default semantics beyond what the schema states.

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 enumerates exactly what the tool returns (users, sessions, page views, key events, bounce rate, avg session duration, with period-over-period comparison, daily series and milestones), so an agent knows precisely what this resource is. It does not, however, name any sibling tool directly, so differentiation from list_pages/list_events is inferred rather than stated.

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?

"Start here for 'how are we doing'" gives clear positive guidance about when this tool is the right entry point, which is meaningful for an overview tool sitting beside many narrower list_* tools. It stops short of naming alternatives or stating when not to use it (e.g. for per-page or per-event breakdowns).

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