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

Annotations already declare readOnlyHint=true, so the description only needs to add context beyond that. It adds that the output includes status and missing items, which is useful, but it does not disclose side effects, permissions, or rate limits. This is consistent with the annotation, so no contradiction.

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, front-loaded sentence that efficiently communicates the action and scope. There is no unnecessary wording, making it highly concise and well-structured.

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 simple list tool with one optional parameter and no output schema, the description is complete: it states what is listed, the scope, and what detail is returned (status and missing). An agent has all the information needed to call it correctly, and the readOnly annotation covers the safety profile.

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?

The single parameter 'site' is fully described in the input schema (coverage 100%). The tool description does not add any parameter semantics beyond what the schema already provides. Baseline 3 is appropriate since the schema covers everything.

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'), resource ('custom domains'), scope ('on this account'), and adds detail ('their status and what is still missing'). It clearly distinguishes from sibling tools like add_domain, remove_domain, and check_domain, which operate on individual domains rather than listing all.

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 that you use this tool to see all custom domains, but it does not explicitly mention when to prefer it over alternatives like check_domain or list_sites. There is no guidance on when not to use it, but the purpose is clear enough that an agent can infer the context.

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