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

Annotations already declare readOnlyHint=true, openWorldHint=false, and destructiveHint=false, so the safety profile is covered. The description's added value is naming the returned data (today's limit, ramp-up, domain DNS health), which tells the agent this is live operational status rather than a static config list. It says nothing about ordering, pagination, or auth requirements, so it adds some but not rich context.

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, zero filler, with the resource named first and the returned data front-loaded immediately after. Nothing redundant and nothing that could be cut without losing 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?

With no output schema present, the description carries the burden of explaining returns and does so at a high level (limit, ramp-up, DNS health). Combined with zero parameters and read-only annotations, an agent has enough to call it correctly, though the exact response shape for each field is still unspecified.

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?

The tool takes no parameters, so the baseline is 4 and there is no schema semantics to compensate for. The description instead characterizes the shape of each returned mailbox entry, which is useful but belongs to return content rather than parameter meaning.

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 ('List mailboxes') and then scopes it: connected sending mailboxes with today's limit, ramp-up, and domain DNS health. This distinguishes it from list_domains, list_campaigns, and list_leads in the sibling set. It stops short of naming a sibling to contrast against, which keeps it off a 5.

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?

There is no explicit statement of when to call this versus alternatives, nor any prerequisites or exclusions. Usage is only implied by the returned fields (limits, ramp-up, DNS health), which suggests an operational health-check context. Adequate but leaves the agent to infer the trigger condition.

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