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

Annotations already signal a write operation (readOnlyHint=false). The description adds useful context — the backend detects the DNS provider and returns records for the user to configure — but omits caveats like reversibility, duplicate-handling, or preconditions. The added value is modest but real.

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 compact sentences with no filler. The core purpose is front-loaded and the behavioral detail follows efficiently.

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 simple one-parameter tool with an output schema present, the description adequately conveys what happens and what the user receives. A minor gap is the lack of connection to email-domain or verification tools, but this doesn't block correct invocation.

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% with a clear type, description, and example ("reports.example.com"). The tool description adds no parameter-level meaning beyond the schema, 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?

"Add a custom domain" is a specific verb+resource statement. The qualifier "custom" and the follow-up about returning DNS records clearly differentiate it from the sibling add_email_domain, which targets a different resource.

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 description implies its use case (adding a custom domain and getting DNS configuration) but gives no explicit when-to-use guidance or alternatives. It does not distinguish itself from add_email_domain or reference related steps like verify_email_domain, leaving selection partly to inference.

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