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

Annotations already declare this is a non-destructive, non-idempotent write and no output schema exists, so the description earns real credit for disclosing the return payload (SPF, DKIM, return-path, DMARC records) and the fact that verification cannot succeed until those records are published. It omits failure modes such as duplicate-domain errors.

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, zero filler, with the core action front-loaded and the consequential return value stated immediately after. Nothing here could be cut without losing information.

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 usefully covers what comes back and the DNS prerequisite, which is the key thing an agent must relay. It leaves the undocumented use_for_any flag and post-creation verification steps unexplained, so it is strong but not exhaustive for a 7-parameter write 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 86%, so the schema already explains name, incoming, outgoing, and all tracking flags; the description adds no parameter-level meaning. It notably never mentions the inbound-email option, which sits slightly at odds with calling it a "sending domain."

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 sending domain" gives a specific verb+resource, distinguishing it from list-domains/get-domain/delete-domain. It doesn't explicitly contrast with update-domain or verify-domain, though "before verifying" gestures at the verify flow, so it stops just short of full sibling differentiation.

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 phrase "to publish before verifying" implies a workflow ordering (create → publish DNS → verify-domain), but there is no explicit statement of when to use this versus update-domain, or what to do if the domain already exists. Usage is inferable rather than stated.

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