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

Annotations already declare readOnlyHint, idempotentHint, non-destructive, and closed-world behavior, so the safety profile is covered. The description adds that it returns a count and sample list, which is useful output context, but it does not describe sample size, pagination, or permission requirements beyond what the schema annotations already imply.

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, and the key action and return content are front-loaded. Every sentence contributes directly.

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 simple read-only preview tool with rich annotations and full schema coverage, the description is nearly complete. It states the return shape ('count + sample list'), which compensates for the missing output schema, though it could say more about sibling alternatives.

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%, so both apiKey and campaignId are already documented in the input schema. The description implies campaignId is the central input but adds no new syntax, format, or constraint information 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 states a specific verb ('Preview') and resource ('recipient set for a campaign'), and adds temporal context ('before sending'). It is clear what the tool does, but it does not explicitly differentiate itself from sibling preview tools like preview_segment or pre_send_review.

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?

The phrase 'before sending' implies the appropriate usage window, but the description does not state when to use this tool versus alternatives such as pre_send_review or preview_segment. It also gives no explicit exclusions or prerequisites.

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