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

Annotations already declare readOnly, idempotent, and non-destructive, so safety is covered. The description still adds value by disclosing that the read returns live external state (apex/www Vercel state, exact DNS records), implying a network-dependent, open-world response, and that the `check` mode is non-mutating.

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 sentences, front-loaded with the resource and the returned fields, then the one notable mode. Nothing is wasted or repeated from the schema.

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's enumeration of returned data (redirect mode, apex/www state, DNS records) is what makes the return value legible, and the `check` mode is explained. What's missing is disambiguation from the domain-related siblings, which matters given how many exist.

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 `id` and `check` are already documented, and the description's note that `check` preflights 'without changes' mostly restates the schema's 'Candidate domain to preflight.' It adds a small amount of meaning but the schema carries the load.

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?

Names a specific verb (read) and resource (custom domain) and enumerates exactly what is returned: redirect mode, apex/www Vercel state, and DNS records. It stops short of naming the sibling tools (check_domain, set_domain, clear_domain) that an agent would otherwise confuse it with.

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?

The second sentence gives a clear condition for the `check` parameter (preflighting a different domain without changes), which is a real usage hint. But there is no guidance on when to call this versus check_domain, set_domain, or clear_domain, and no stated prerequisites such as a selected site id.

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