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

The annotations flag openWorldHint=true and readOnlyHint=false; the description adds real context beyond them, namely that this is a state-advancing mutation on an already-added domain rather than a pure DNS read. It does not explain what happens on verification failure or whether the operation is retried safely, so it falls short of 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?

Three short sentences, with the action and its scope front-loaded before the pointer to the instructions tool. The version trailer is boilerplate but earns its place because the schema requires that exact value.

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?

No output schema exists, so the description should say what a verification call returns (for example, which DNS records are missing or the pending status), but it doesn't. It also leaves out prerequisites such as whether the domain must first be added or the app deployed.

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 app_id and domain are already fully documented. The description echoes both names and restates the mcp_version value ('2.12'), which is redundant with the schema's own instruction to set that same value, so it adds little beyond the schema baseline.

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 specific verb and resource: it checks DNS and advances an 'existing domain connection' toward activation. Using 'existing' implicitly distinguishes it from add_custom_domain, though the sibling is never named directly.

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 states the required inputs (app_id, domain) and routes the agent to get_custom_domain_instructions for the workflow. It doesn't say when the call will fail or when not to call it, so the condition is clear but the exclusions are absent.

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