Create mailbox

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

Annotations already declare the mutation profile (readOnly=false, destructive=false, openWorld=true), and the description adds substantial non-obvious behavior: a verification email is sent, the mailbox starts unverified, and it cannot own aliases or become the default until the link is clicked. This is exactly the kind of side-effect detail the schema cannot convey.

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-loads the core action, then layers the verification consequence, the cross-reference to mailbox_list, and the plan caveat. Every sentence earns its place with no filler.

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?

No output schema exists, but the description compensates by explaining the async verification outcome and pointing to mailbox_list for status. For a single-parameter creation tool, an agent has everything needed to call it correctly and interpret the result.

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 100% and the schema already documents the email parameter including its role in receiving the verification email. The description adds no syntax or format detail beyond what the schema provides, so the baseline 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?

States a specific verb (Add) and resource (mailbox), and even disambiguates the concept by defining it as 'a real email address that receives alias mail.' This clearly separates it from siblings like mailbox_list, mailbox_update, and mailbox_delete.

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?

Provides clear operational context: it names mailbox_list as the follow-up to check verification status and notes premium-plan implications for additional mailboxes. It stops short of an explicit when-to-use-vs-alternative statement, but the surrounding workflow is well implied.

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