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

Annotations already indicate read-only, idempotent, non-destructive behavior, so the description does not need to restate those. It adds value by noting the plan requirement and the time-series nature of the metrics, but it does not disclose return shape, granularity, or any limits, which the absent output schema otherwise leaves uncovered.

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 no filler. The metric breakdown is front-loaded, and the plan requirement is placed second, so an agent can quickly decide whether this tool is relevant before reading further.

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 single-parameter, read-only analytics tool, the description covers the essential information: which metrics are returned, the per-campaign scope, the time dimension, and the plan prerequisite. It does not describe the exact response format, but the low complexity and strong annotations make this 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 coverage is 100% and campaign_id is simply described as 'Campaign id'. The description adds minimal extra meaning by confirming this is for one campaign, but it does not explain how the ID maps to the response or provide format details beyond the schema.

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 clearly identifies what the tool covers: open, click, reply, and bounce breakdown over time for a single campaign. It stops short of using an explicit verb like 'retrieves' or 'returns', and it does not explicitly distinguish itself from the sibling get_campaign_stats, though the metric set and 'over time' imply a more detailed analytics view.

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 gives useful context: this is for one campaign and requires a plan with campaign analytics. It does not explicitly state when to prefer this over get_campaign_stats or other analytics-adjacent tools, but the single-campaign scope and prerequisite make the intended use reasonably clear.

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