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

Annotations already declare this is a non-read-only, non-destructive, non-idempotent, closed-world write. The description adds behavioral context the annotations cannot carry: the account-level plan cap on active mailboxes and the permanent-vs-rotating semantics of each domain. It does not note whether repeated calls are cheap or whether domain rotation is per-request.

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 purpose, then the quota constraint, then the domain list. The domain enumeration is long but earns its space because the values are not expressed as a schema enum. No filler sentences.

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?

With no output schema, the description partially compensates by showing the address format that results from a successful call, plus the domain trade-offs. It does not state what the response body contains (e.g. the mailbox id needed for later read/delete calls), which a for a creator tool would be useful.

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 goes further by enumerating the concrete domain values and labeling which are permanent versus rotating — information absent from the schema (no enum present). This meaningfully informs domain selection.

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 ('Create a new disposable inbox') and immediately describes the artifact it produces, including the address shape. An agent can distinguish it from list_mailboxes, delete_mailbox, and restore_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?

Gives real usage context: plan-limited concurrent mailboxes and the advice to delete one to free a slot, which explicitly routes to the delete_mailbox sibling. It stops short of saying when to prefer restore_mailbox over creating a fresh inbox, so it is clear but not exhaustive.

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