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

Annotations already declare readOnly=false, destructive=false, idempotent=false and openWorld=false, so the agent knows this mutates state but is not flagged destructive. The description adds that the call returns DNS records to add, which is useful behavioral context absent from the annotations. It does not address non-idempotency (what happens on repeat calls) or interaction with already-existing domains, leaving a real gap for a mutation tool.

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?

Compact – three short sentences, with the core action front-loaded. The phrase "in one step" duplicates the title and the quoting style around the layout keywords is slightly awkward, but no sentence is wasted.

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?

There is no output schema, and the description correctly covers the return value (DNS records). Layout semantics are well covered, but for a non-idempotent mutation tool the description is silent on limits, repeat-call behavior, and how it interacts with pre-existing domains or the sibling add/verify tools – a moderate completeness gap rather than a fatal one.

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 67%: root and region are documented in the schema, but layout is a bare enum with values only. The description carries the semantic burden for layout by explaining what each preset actually configures (root/news./reply. vs everything on mail.), which the schema cannot convey. Region's meaning remains schema-only, which is acceptable.

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 states a concrete verb and resource: it adds email domains in one step using a preset layout. It implicitly distinguishes itself from single-domain siblings like add_mail_domain or register_mail_domain by emphasizing the one-step/batch nature, but it never names those alternatives explicitly, so sibling differentiation is left to inference.

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 real usage context for choosing between layouts ("recommended" for a full setup, "single" for a Resend plan with few domains), which is genuinely helpful. However, it offers no guidance on when to use this tool versus add_mail_domain/register_mail_domain, nor any prerequisites (e.g., domain already verified, existing domains present).

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