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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so the safety profile is covered. The description adds useful authorization context ('any member of the business can read') and notes the consent/do-not-email filtering on returned customers, which is behavioral detail beyond the structured fields.

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 read purpose, then the parameter routing, then the read-only/auth note. Every clause earns its place, though the middle sentence packs a dense list of returned fields that could be tightened.

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?

An output schema exists, so return-value exposition is optional, yet the description still summarizes what comes back, plus auth scope and the three input modes. Nothing an agent needs to call this correctly is missing.

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 67% (business_id is undocumented in the schema), so the description carries real weight by explaining the optional-branch semantics of campaign_id (one campaign) and sender_id (domain DNS records). It adds mode meaning beyond the schema's terse descriptions, though it does not restate business_id, which is already required.

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 ('Read') and resource ('email campaigns') and enumerates exactly what the response surfaces: sending addresses with setup readiness, recent campaigns with status and outcome counts, and email-eligible customers. This lets an agent distinguish it from siblings like list_campaigns, create_campaign, and email_campaign without opening any schema.

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 description gives clear mode-selection guidance: pass campaign_id for a single campaign, or sender_id for that domain's DNS records. It does not, however, contrast the tool against list_campaigns or the single-campaign view siblings, so the routing decision between tools is left partly to inference.

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