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

Annotations already disclose this is a non-readonly, non-idempotent, non-destructive mutation. The description adds one genuinely valuable behavioral fact not in the annotations: the API key is shown only once, which implies irreversibility after the call. It omits other relevant traits such as required permissions, whether the domain must be verified, and quota implications.

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, front-loaded with the action and followed by the one non-obvious fact (one-time API key). 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?

There is no output schema, and the description does not describe the returned inbox object or clarify whether the API key is returned in the same response. It also leaves out prerequisites for a non-idempotent create on a domain. Adequate but with clear gaps for a creation 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?

Schema coverage is 75%, with orgId, domainId, and localPart each documented (including a localPart example), so the schema does most of the work. The description only implies the localPart@domain composition and adds no syntax or constraint detail beyond the schema; unchanged baseline of 3 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?

States a specific verb and resource ('Creates an inbox') plus the scoping detail that the address is chosen on a domain. It is clear in itself, but it does not distinguish itself from the sibling mailbox_create, which an agent could easily confuse with inbox creation.

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?

No guidance on when to use this vs mailbox_create, no prerequisites stated (e.g. the domain presumably needs to be attached/verified first, given domain_attach/domain_verify exist), and no mention of alternatives or exclusions. The description only describes the action, not the decision to take it.

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