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

Annotations already declare readOnlyHint=false, openWorldHint=true, idempotentHint=true and destructiveHint=false, but the description goes well beyond them: it discloses the DNS dependency, the conditional mutation of the page, the Premium entitlement requirement, and the transient propagation failure mode with an explanation that it is normal. That is exactly the operational context an agent needs before retrying or reporting an error.

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 short sentences, each carrying distinct information: the action, the entitlement gate, and the expected failure window. The action is front-loaded and there is no filler.

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?

Since an output schema exists, return values need not be described, and the description covers the mutation, the gate and the failure mode. The remaining gap is the success-vs-mismatch branch (what happens when the DNS record points elsewhere) and how it relates to the get/set/remove_custom_domain siblings.

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 0% for the single 'domain' string parameter, so the description has to compensate. It clarifies that the value is looked up in DNS, but adds no format guidance (bare hostname vs URL, subdomain handling or TLD expectations), leaving the agent to guess at input shape.

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 gives a concrete verb chain (DNS lookup, then switch the page to the domain) that makes the tool's job unmistakable. It does not explicitly differentiate itself from the sibling set_custom_domain or get_custom_domain, which it sits between conceptually, so the boundary is left for the agent to infer.

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 implies the tool is used after the domain record exists ('fails until the record has actually propagated') and notes it is Premium-gated, which is useful eligibility context. However, it never states when to use this versus set_custom_domain or get_custom_domain, and gives no explicit when-not condition.

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