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

Annotations already declare it is a non-read-only, non-idempotent, open-world write. The description adds two useful facts beyond them: the paid-plan requirement and that it initiates a DNS connect session (implying a multi-step flow). It does not disclose that the connect is asynchronous or what the completion step is, so the picture remains partial.

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 tight sentence with the plan constraint and the session outcome front-loaded; every clause earns its place. It is arguably over-terse for a mutation with follow-up steps, but 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?

With 100% schema coverage and annotations carrying the safety profile, the definition is callable as-is. However, for a domain-connect flow the agent lacks the crucial next-step and polling context, and no output schema exists to fall back on, leaving the workflow incomplete.

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 100%: site, hosts, domain, context, and guestToken are each fully documented in the schema, including the hosts-vs-domain fallback and the guestToken lifecycle. The description adds no parameter-level meaning, so the 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?

The description names a specific action (connect apex and/or www) and the initiating effect (starts a DNS connect session), which distinguishes it from read-side siblings like get_custom_domain_connect and list_custom_domains. It stops short of explicitly differentiating from refresh_custom_domain, reapply_custom_domain_oauth, or set_primary_custom_domain, so it is clear but not sibling-aware.

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?

"on a paid plan" gives one precondition, but there is no guidance on when to prefer this over refresh/reapply/set_primary, nor any statement of what the caller must do next (e.g., wait_for_custom_domain). Usage is implied by the action rather than explained.

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