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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered; the description adds that the 'check' path makes no changes, reinforcing the non-mutating nature beyond the annotations. It stops short of describing anything about freshness or failure behavior, which keeps it from a 5.

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 tight sentences, with the primary resource and returned data front-loaded and the secondary 'check' mode appended. Every clause carries information and nothing is redundant.

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 read-only, no-output-schema tool, the description adequately conveys what comes back (redirect mode, apex/www state, required DNS records), so an agent can act without opening the schema. It is not fully complete on how to interpret or act on those records.

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 the baseline is 3. The description goes slightly beyond the schema's terse 'Candidate domain to preflight' by clarifying that check performs a side-effect-free preflight, adding real semantic value for that parameter.

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 ('Read the site's custom domain') and enumerates the payload fields (redirect mode, apex/www Vercel state, DNS records), so an agent immediately knows what it returns. It does not, however, distinguish itself from the sibling 'check_domain' or 'set_domain' tools, which keeps it below a 5.

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?

Usage is only implied: the 'check' clause hints at a preflight use case for another domain, but there is no explicit when-to-use guidance, no when-not, and no routing to the similar 'check_domain' sibling. The agent must infer context.

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