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

Annotations already declare readOnlyHint=true and openWorldHint=false, so safety is covered structurally. The description usefully clarifies that results are scoped to what the connection can operate and include the domain, but adds nothing about ordering, pagination, or volume.

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 waste, with the what-is-returned content front-loaded before the call-ordering advice.

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 and no parameters, the description does the necessary work by stating that each result carries its domain, and directs first-call usage. Nothing critical is missing for a zero-argument listing 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?

The schema accepts zero parameters, so per the rubric the baseline is 4. The description correctly implies no filtering input is 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 and resource ('List every mailbox') and adds the result's scope ('this connection can operate, with its domain'). It is clear on its own, though it never explicitly distinguishes itself from the sibling search_all_mailboxes.

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 an actionable ordering directive ('Call this first instead of guessing addresses'), which tells the agent when to invoke it. It stops short of naming the alternative search_all_mailboxes as the tool to use when you already know the address.

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