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

With no annotations provided, the description carries the behavioral disclosure burden. It clearly states that authentication is required and indicates a read-only listing operation via the verb 'List', while also surfacing the expected status values (PENDING_DNS or ACTIVE) and DNS mode. It does not discuss pagination or failure behavior, but these are minor for a simple list tool.

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 a single focused sentence that front-loads the core action and resource, then adds the key output details and authentication requirement. There is no redundant or vague wording.

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 low-complexity tool with one optional parameter and no output schema, the description adequately conveys the entity being listed, the filtering condition, output fields, and authentication. It does not describe the full response shape or explicitly compare with listUserDomains, but those gaps are minor given the tool's simplicity.

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 description coverage is 100%, so the input schema already fully explains the sessionKey parameter. The tool description adds no additional parameter-level meaning beyond what the schema provides, so the baseline of 3 is appropriate.

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 states a specific verb ('List'), a clear resource ('your domains that are enabled for email hosting'), and the relevant output fields (status and DNS mode). This distinguishes it from sibling tools like listUserDomains, which likely lists all domains, and listMailboxes, which lists mailboxes rather than domains.

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 implies when to use the tool: when you need email-enabled domains and their DNS status. However, it does not explicitly name alternatives or state when not to use this tool versus listUserDomains or listMailboxes, leaving some routing to inference.

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