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

Annotations already signal the operation is mutating and non-destructive. The description adds meaningful behavioral context by distinguishing creation from resumption of a pending mailbox and by declaring a domain-scope invariant. It does not go into retry/idempotency behavior, but that is partly covered by the idempotencyKey schema descriptions and idempotentHint=false annotation.

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?

The description is compact and front-loaded: one sentence states the full purpose and the two modes, and a second short sentence adds an important safety constraint. There is no filler or unnecessary repetition of schema content.

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 tool with two oneOf branches, an output schema, and useful annotations, the description is nearly complete: it explains both branches, the domain invariant, and maps naturally to the input schema. A small gap is that it does not explicitly say that the mailboxId branch is for resuming while the localPart branch is for creating, but that is inferable from the branch definitions.

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?

Parameter semantics are already well documented in the input schema: localPart, displayName, mailboxId, and idempotencyKey each have descriptions. Since schema description coverage is reported as 100%, the description reasonably does not repeat parameter details, so the baseline score applies.

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 names a specific verb ('Create and prepare' / 'resume') and a distinct resource ('mailbox in the account domain'). It also clarifies the two supported modes and adds the boundary 'Never changes the account domain,' making it easy to distinguish from the email-oriented siblings in the tool list.

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 context: use this tool to create a new mailbox or resume an existing pending one. It includes a useful exclusion in 'Never changes the account domain,' though it does not explicitly name alternative tools or spell out when not to use it beyond that boundary.

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