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

Annotations already declare readOnlyHint=true, so safety is covered. The description adds real value by disclosing what the response contains (engagement metrics), which matters because there is no output schema, plus the exact REST endpoint for API-level mapping. It omits error behavior for missing/unsent campaigns.

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 compact sentences that are front-loaded with the purpose and metrics, followed by the endpoint mapping used as a reference hook. No filler or repetition.

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 tool whose annotations cover the safety profile, the description gives enough to invoke correctly and preview the return payload. With no output schema, the metric list is a reasonable stand-in, though edge-case behavior is undocumented.

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 with 100% schema description coverage, so the schema already documents campaign_id fully. The description adds nothing about the parameter beyond what the schema states, making the baseline 3 appropriate.

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 the report for one campaign') and enumerates the metrics returned (opens, clicks, bounces, unsubscribes). The singular scope distinguishes it from the sibling mailchimp_list_reports, and the REST path pins the exact underlying resource.

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 only implied: an agent can infer you call this when you need engagement stats for a known campaign_id. It never says when to prefer this over mailchimp_get_campaign or mailchimp_list_reports, nor states prerequisites (e.g., that a campaign must have been sent).

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