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

The annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so the safety profile needs no restating. The description adds genuine context beyond that: plan gating (Pro or higher) and the fact that verification/SSL status is included in the result. It does not address result size or ordering for accounts with many domains.

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?

Two sentences with no waste: the output content leads and the access requirement follows. Nothing is padded or restated from the title.

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 zero-parameter read tool with full annotation coverage, the description covers what it returns and who can call it, which is essentially everything an agent needs. The only minor gap is the absence of any hint about how to act on the returned verification/SSL status (e.g., pointing at verify_domain).

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 tool takes zero parameters, so there is nothing for the description to disambiguate; the baseline of 4 applies. The description correctly does not invent filtering or pagination options that the empty schema does not support.

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 and resource ("List your custom domains") and adds the returned attributes ("verification/SSL status"). This clearly separates it from mutating siblings such as add_domain, delete_domain, verify_domain, and update_domain, though it never names any of them explicitly.

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?

It supplies a real prerequisite ("Requires Pro or higher"), which tells the agent whether the call is available. However, it gives no explicit when-to-use guidance or pointers to alternatives like verify_domain or activate_domain when a domain is unverified.

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