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

Goes beyond the annotations by disclosing the auth requirement (account token) and the billing consequence ('Does not charge'), plus who completes the loop (the account holder confirms from that email). It does not explain rate limiting or what happens on repeated calls, which matters given idempotentHint=false, but the added context is substantive.

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 short sentences, front-loaded with the precondition and the core action, with zero filler. 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-parameter, non-idempotent email-trigger tool with no output schema, the description covers the action, the auth need, and the cost implication. What the call returns or whether it can be re-triggered freely is left unspecified, but the essentials for correct invocation are present.

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 description coverage is 100%, so both parameters (site and domain) are already fully documented with examples. The description adds no further semantics about their formats or relationship, which is acceptable at this coverage level.

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 (resends) and resource (the registry's owner-confirmation email for a domain registered here), which cleanly separates it from the similarly-named sibling resend_receipt. An agent can identify the operation without opening the 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?

The scenario is implied — the account holder has not yet confirmed ownership and the email must go out again — and the parenthetical '(needs account token)' signals the precondition. However, it never explicitly states when to use this versus alternatives (e.g. asking for status via email_status) or when it should not be called.

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