create_mailbox

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

Goes well beyond the readOnlyHint=false/destructiveHint=false annotations: it discloses missing-parent auto-creation, the '%' rejection rule, Gmail label behavior and the move_mail refusal (#291), that reads show the new label empty, and the required Automation plus Full Disk Access permissions for 'On My Mac'.

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?

Purpose and the required-account rule are front-loaded, then return shape, token semantics, and caveats. It is dense but nearly every clause carries operational information; the Gmail-label parenthetical is the only passage that verges on over-long.

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?

Despite an output schema, the description still names the return fields and, critically, explains that the returned 'folder' token works immediately while mail_overview reports a different spelling later — a non-obvious detail an agent would otherwise get wrong. Permissions and platform caveats are covered.

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 0% with two required, undescribed string parameters, so the description must carry the load and does: 'name' supports '/' nesting and rejects '%'; 'account' accepts a display name, a UUID, or 'On My Mac'. That is exactly the disambiguation an agent needs to construct a valid call.

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 Mail mailbox (folder) under one account') and clarifies the folder concept, distinguishing it from message-creation siblings like create_draft. The scope ('under one account') and nesting semantics are unambiguous.

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 concrete usage conditions: 'account' is REQUIRED and why, the 'folder' token is what to pass to move_mail/mail_search, and it explicitly closes off the wrong expectation with 'There is no delete counterpart... do it in Mail.' No competing creation tool exists to disambiguate against, so no explicit alternative routing is needed.

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