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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the description focuses on what annotations cannot convey: the paid-account requirement, the delivered-only precondition, and the raw endpoint. It doesn't explain behavior on invalid/undelivered campaigns or stats freshness, which is the remaining gap.

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 outcome and the precondition, then the metric list, then the endpoint. The long metric enumeration earns its place because there is no output schema; the raw REST path is marginal but small overhead.

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 stands in for the return shape by naming every metric. Preconditions and the paid-account gate are covered; only error/freshness behavior is missing, which is minor for a single-parameter read tool.

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 the schema documents it fully at 100% coverage as 'Campaign id.' with a positive-integer bound. The description adds no extra meaning about where the campaign_id comes from (e.g., from list_campaigns), so 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 specific verb and resource ('Delivery results of a DELIVERED campaign') and enumerates the exact metrics returned, which distinguishes it from campaign-management siblings like list_campaigns or send_campaign. An agent immediately knows this is a read-only post-send reporting call.

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 clear preconditions: the campaign must be in DELIVERED status and a paid account is required. It does not name alternatives or exclusions (e.g., what to call for an un-sent campaign), but the context for use is unambiguous.

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