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

Annotations already declare readOnlyHint=true and destructiveHint=false, so "changes nothing" is largely redundant. The description does add real value beyond the annotations, though: it discloses that both apex and www are checked and that the response reports free/attached/erroring state plus required DNS records.

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?

A single sentence with zero filler; the core verb and scope are front-loaded and the non-mutating guarantee is tacked on efficiently at the end.

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?

With no output schema, the description carries the return-value burden and does so (free/attached/erroring, DNS records to add). Combined with annotations covering the safety profile, nothing essential for correct invocation is missing.

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 coverage is 100%, so both parameters are already documented. The description clarifies that the domain argument is a "candidate" (not the attached) domain but adds no syntax or format beyond the schema, so baseline 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?

"Preflight a candidate domain (apex + www)" gives a specific verb-like action, a precise resource scope, and the outcomes checked (free/attached/erroring). It clearly reads as a non-mutating inspection, but it never names the closest sibling (get_domain_status) so the agent must infer the distinction itself.

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?

"Preflight a candidate domain" and "Changes nothing" place it squarely in the pre-set_domain validation slot, giving clear usage context. However it names no exclusion or alternative, so an agent choosing between this and get_domain_status gets no explicit routing rule.

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