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

Adds behavioral context beyond annotations: describes it resolves a count and previews content without sending. Annotations already indicate readOnlyHint=true and no destruction, so description reinforces safety without contradiction.

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 sentences, front-loaded with key verb and action, no redundant or extraneous information.

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?

Given low complexity (1 param), rich annotations, and presence of output schema, the description fully explains the tool's purpose and behavior without needing to detail return values.

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 (campaignId) with description already in schema. Schema coverage is 100%, so baseline of 3 applies; description adds no additional meaning beyond 'Campaign ID to validate'.

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?

Clearly states the verb 'validate' and the resource 'campaign', with specific actions (resolving contactable recipient count, previewing subject/body) that distinguish it from sibling tools like create_campaign or send_campaign.

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?

States 'before sending', providing clear context for when to use. However, no explicit when-not-to-use or alternatives among siblings (e.g., vs. update_campaign or list_campaigns) are mentioned.

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