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

With annotations covering only the safety profile, the description adds substantial operational context: setup enables provider receiving but returns only child MX instructions without touching DNS/sending/tracking, existing reply destinations cannot be replaced, verification auto-refreshes and fails closed after seven days, and no email is sent or permission granted. These are real behavioral traits an agent cannot derive from the structured fields.

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?

Purpose is front-loaded, then prerequisites, then action semantics and caveats, with no filler sentences. The telegraphic fragment style is dense and occasionally hard to parse, but every clause carries 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?

For a two-action, nested-payload tool with no output schema, the description covers the workflow, prerequisites, side-effect boundaries, expiry behavior and a pointer to a guide. It is nearly complete; only explicit sibling routing and return-shape expectations are missing, which is minor since setup's MX output is described.

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% and the payload is an opaque nested object, so the description compensates by naming the required fields (domainId, connected replyDomainId, expectedRevision, stable requestId) and tying them to the setup/verify actions. It also clarifies that identity comes from the connected account, which the schema only hints at.

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 (configure a branded email reply domain) and enumerates the two actions, setup and verify, so an agent knows the shape of the operation. It does not explicitly contrast itself with near siblings like inspect_email_reply_domain or configure_email_tracking, leaving some differentiation 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?

Gives an implied but clear sequence: connect the child domain through ordinary domain setup first, then use setup, add MX records, then verify. It also notes normal domain allowance applies and points to a workflow guide resource. It stops short of naming alternate tools or stating when not to use this one.

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