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

With no annotations provided, the description carries the full burden. It discloses that the tool returns DNS records, that publishing them typically requires a human with registrar access, and that sending is blocked until verification succeeds. These are meaningful behavioral traits beyond the schema, though it does not mention idempotency or error behavior for duplicate calls.

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 sentences, each purposeful: the first states the core action and output, the second gives operational advice, and the third names the verification dependency. No filler or repetition.

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 one-parameter tool with no output schema and no annotations, the description explains the registration flow, DNS record output, and the verification prerequisite. It is complete enough for an agent to know what to expect and when to invoke it, though it does not describe the exact structure of the returned DNS records.

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 the parameter description already fully documents 'name' as a bare domain and recommends a subdomain. The tool description adds nothing about the parameter format or meaning beyond what the schema provides, 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 uses a specific verb ('Register') and resource ('a domain to send from'), and clearly separates this from sibling tools by explaining it produces DNS records and is a prerequisite for verify_domain. An agent can immediately distinguish this from list_domains, verify_domain, or send_email.

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 gives practical timing guidance ('start this early'), notes the human-in-the-loop DNS requirement, and explicitly states the domain cannot send until verify_domain succeeds. This is clear context for when to use add_domain, though it does not explicitly contrast it with sibling tools beyond verify_domain.

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