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

The description adds the behavioral constraint 'Never changes the account domain,' which is valuable beyond the annotations. However, it doesn't elaborate on other behaviors such as idempotency (despite the idempotencyKey), what happens if the mailbox already exists, or any side effects beyond the domain constraint. With annotations covering safety hints, this is adequate but not rich.

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 two sentences with zero waste. It front-loads the primary action and adds a critical constraint in the second sentence. No irrelevant details are included.

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?

The description covers both operational modes (create and resume) and the domain constraint. The schema fully documents the parameters, and an output schema exists to explain return values. Given the tool's simplicity and the richness of the schema, nothing essential 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?

The input schema provides detailed descriptions for all parameters (localPart, displayName, idempotencyKey, mailboxId), and the schema coverage is 100%. The tool description does not add any additional parameter semantics beyond what the schema already states, so the baseline of 3 is appropriate.

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 clearly states the tool creates or resumes a mailbox in the account domain, with the explicit constraint that it never changes the account domain. This distinguishes it from other mail-related tools like send_email or create_folder, making its purpose unambiguous.

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 provides clear context on when to use this tool: when you need to create or prepare a mailbox or resume a pending one. It doesn't explicitly mention alternatives or exclusions, but the purpose is so specific that an agent can infer the appropriate usage without confusion.

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