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

Annotations only declare basic safety hints, while the description adds critical behavior: returns IMAP/SMTP credentials, password shown only once, quota limits, and post-creation restrictions for agent-kind keys. This is substantial context beyond what annotations provide.

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?

Five sentences, front-loaded with purpose, then return values, rate limit, permission implications, and displayName guidance. Every sentence earns its place with no redundancy.

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 creation tool with no output schema, the description covers return values, one-time credential exposure, quota limits, and permission consequences. An agent has enough context to call it correctly without needing further documentation.

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. The description adds marginal meaning beyond the schema by noting that omitting displayName causes recipients to see only the bare address, and it reiterates the domain constraint, but it adds no detail for localPart.

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 the specific verb and resource ('Create a new mailbox (email address)') and adds scope ('on a domain the account controls'). This clearly distinguishes it from siblings like list_mailboxes or update_mailbox without opening any schema.

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 prerequisites (domain must be on the account), rate limit (10 mailboxes per key per 24h), and agent-key permission behavior after creation. It does not explicitly name an alternative tool such as create_alias, so it falls short of full when/when-not routing guidance.

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