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

The annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false, and openWorldHint=false, so the safety profile is fully covered structurally. The description adds a genuinely useful behavioral trait beyond the annotations: the tool is gated behind a Premium plan, which can explain invocation failures for free-tier users.

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 short sentences with zero filler. The core read behavior is front-loaded and the Premium constraint is a compact trailing qualifier.

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?

An output schema exists, so the description need not explain return values, and the annotations carry the safety profile. For a zero-parameter read tool this is nearly complete; the only real gap is the absence of guidance distinguishing it from verify_custom_domain and the other 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?

The tool takes no parameters, so there is nothing for the description to clarify at the parameter level. Baseline of 4 applies; the description correctly spends no words restating an empty schema.

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?

States a specific verb ('Read') and resource ('custom domain') and defines the two pieces of information returned: connection status and required DNS record. This is far more specific than the title, but it does not explicitly differentiate from close siblings like verify_custom_domain or get_page_settings, leaving some overlap to inference.

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?

There is no when-to-use or when-not-to-use guidance. The description never explains how this differs from verify_custom_domain or remove_custom_domain, nor when an agent should call this versus set_custom_domain. 'Part of Premium' is an availability note, not usage guidance.

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