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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the safety profile is covered. The description adds genuine value by stating that read scope is required, which the annotations do not express. However, it says nothing about return granularity (time series vs. aggregate), pagination, or what "over time" produces, so behavioral context remains thin.

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 with the action front-loaded and no redundant wording. It is efficient, though "over time" is vague enough to cost a point of precision rather than adding clarity.

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 two-optional-parameter read tool with no output schema, the essentials are present, but the description never clarifies what the metric dimensions are or how the time window shapes the result. An agent can call it, but cannot predict whether it returns a series, a summary, or per-campaign breakdowns.

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 both days (1–90, default 30) and campaign_id fully documented in the schema. The description adds no meaning beyond that, 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?

States a specific verb and resource ("get email performance metrics over time"), which is more precise than the bare name. It does not distinguish itself from nearby siblings such as get_engagement_metrics, get_response_time, or get_campaign_analytics, so an agent cannot tell from the text alone which metric tool to pick.

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?

There is no statement of when to use this tool versus alternatives, no mention of the metrics siblings, and no note that campaign_id may narrow or broaden scope. The only guidance is a bare permission requirement.

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