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

Annotations already declare readOnlyHint=true and openWorldHint=false, so safety is covered. The description adds genuinely useful non-obvious context: the response is aggregated in one call, days are UTC, and the absent opens metric is a deliberate product limitation rather than a bug. It still says nothing about result size, pagination or permission requirements.

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?

Three sentences, each doing work: first enumerates the return payload, second gives the use case, third preempts a likely confusion about the missing opens metric. Front-loaded and free of 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?

No output schema exists, so the description carries the return-value burden and does it well by listing every section of the response. Combined with annotations covering the read-only profile, an agent has everything needed to call this correctly with a single campaign ID.

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?

Only one parameter, and schema description coverage is 100% — the schema already says it is the numeric campaign ID from list_campaigns. The description adds no syntax, format or edge-case guidance beyond that, so the baseline 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 precise verb and resource and enumerates the exact payload: totals, per-A/B-variant results, per-sequence-step results and a daily UTC time series. This is far more specific than a generic 'get stats', though it never names a sibling (e.g. get_campaign vs get_outcomes_report) to explicitly draw the boundary.

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?

Gives a clear use context: 'Use it to judge how a campaign is doing or to compare variants.' That tells the agent the intent, but there are no exclusions or named alternatives for when a different report tool would be the better choice.

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