List Mailboxes

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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, non-open-world), so the description's job is to add domain behavior - and it does: it explains the PENDINGSETUP/null-address state, the free trial mailbox every registration includes, and that price/mail-client settings come back. It stops short of noting auth scope or pagination, so it is strong but not exhaustive.

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?

Three tight sentences, front-loaded with the verb and resource, then the state semantics, then the secondary return values. Information density is high and nothing is wasted, though the parentheticals make it slightly dense for a simple list operation.

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, so the description must carry the return-value burden, and it names the fields returned (status, address, trial, expires, autoRenews, renewalPrice, price, client settings). Combined with the one-parameter schema, an agent has everything needed to call and interpret this 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?

Only one parameter and schema coverage is 100%, with the schema already giving the FQDN format example. The description adds no syntax or constraint beyond confirming the domain is the mailbox host, so the 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 ('List a domain's email hosting mailboxes') and immediately scopes what a mailbox is (real inboxes at the domain, read over IMAP/POP or webmail). It also names the sibling actions setup_mailbox and renew_mailbox, so an agent can distinguish the read path from the mutating paths.

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 ties the listing to concrete follow-up decisions: a mailbox with status PENDINGSETUP and address null is handled by setup_mailbox, and autoRenews/renewalPrice are handled by renew_mailbox. That gives clear context for when this tool is the entry point, though it never states an explicit exclusion or a 'use X instead' routing rule.

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