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

Annotations already declare the mutation profile (readOnlyHint=false, destructiveHint=false, idempotentHint=false, openWorldHint=false). The description adds the scenario that motivates the call, but says nothing about what the call does to the existing domain record, whether DNS/verification state is preserved, or what happens if the domain still exists in Resend — gaps that matter for a non-idempotent write.

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?

A single efficient sentence with the qualifying scenario front-loaded after the action, and no filler. Slightly awkward compression ('HelpWell knows') keeps it just short of ideal.

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 one-parameter tool with full schema coverage, annotations covering safety, and no output schema, the description is adequate but thin: it omits where domainId comes from and the observable outcome (does the domain return in a pending/verified state?). Those are the remaining facts an agent would need.

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?

Only one parameter and schema description coverage is 100%, so the schema already documents 'domainId'. The description implies the id refers to a domain known in HelpWell but doesn't say where the agent obtains it (e.g., list_resend_domains vs. an internal listing), so no lift beyond the schema baseline.

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 and resource ('Add a domain ... back to Resend') and scopes it to a precise scenario: a domain HelpWell already knows but Resend no longer has. That scenario differentiates it from the sibling 'add_mail_domain' by implication, though it never names the alternative outright.

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 a concrete when-to-use condition (the domain was deleted in Resend but still exists in HelpWell), which is exactly the discriminator an agent needs against add_mail_domain / reuse_resend_domain / update_mail_domain. No explicit when-not or named alternative, so it stops short of a 5.

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