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

Annotations already declare non-readonly, non-destructive, non-idempotent and open-world, and the description adds real value on top: it discloses the return payload (DNS records with type, host, value, status, next action) and that verification is asynchronous and deferred to a later call. Missing are failure modes such as duplicate-domain behavior or permission requirements.

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, front-loaded with the action and auth purpose, then the return shape, then the follow-up step and the dry-run escape hatch. No sentence is filler.

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, and the description compensates by enumerating the returned DNS record fields and the required follow-up action. Combined with 100% param coverage and full annotations, an agent has everything needed to call and interpret this tool.

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 parameters are already fully documented, including the dry_run semantics the description merely restates ('validate without adding'). The only added nuance is framing domain as authentication-related, which is marginal — 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?

States a specific verb+resource (add a sending domain) plus the authentication purpose (SPF, DKIM, DMARC), and implicitly distinguishes itself from the read-side siblings get_domain/list_domains by being the creation step. An agent can identify it without opening any schema.

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?

Explicitly sequences the workflow: add here, publish the returned records, then verify with get_domain, and offers dry_run:true for a non-mutating check. It gives clear context and a named alternative, though it never states when NOT to use it (e.g. domain already exists, use list_domains first to check).

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