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

Annotations already declare readOnlyHint=false and destructiveHint=true; the description does not contradict them. It adds valuable behavior beyond the flags: writes go to a shared AgentMail workspace visible and editable by other callers, created inboxes are real send/receive addresses, and usernames may be generated.

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 dense and front-loaded, with each sentence adding a distinct piece of information: creation semantics, username behavior, domain restriction, return values, workspace sharing, and follow-up tools. It is longer than a minimal description, but the extra length is justified by the shared-workspace warning and parameter nuances.

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?

Given the full schema coverage, rich output schema, and meaningful annotations, the description covers everything an agent needs to call this safely: what creation does, how addresses are generated, the shared-state side effect, and how to verify the result. No critical usage or behavioral context 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?

Schema coverage is 100%, so the baseline is 3, but the description adds real semantic value for username and domain: it explains the local-part behavior with examples and states that the domain is always agentmail.to because domain management is not exposed. Other parameters are adequately covered by the schema.

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 opens with 'Creates a new inbox — a real address that can send and receive,' giving a specific verb, resource, and capability. The 'real address' framing clearly distinguishes it from draft-only tools, and the domain/username details further narrow the purpose.

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 useful usage guidance: how to choose a username, that the domain is fixed to agentmail.to in this context, and which read/list tools to use afterward. It does not explicitly say when to prefer this tool over post_agentmail_inbox_draft or patch variants, but the core usage context is clear.

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