plan_mail_setup

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

Even though there are no annotations, the description fully discloses the side effect: it may create a sending domain in the operator's own Resend account, while making no changes to the client's DNS. This is transparent about the one write operation.

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?

The description is somewhat repetitive and rambling, but it is front-loaded with the main purpose and each sentence adds useful detail. The overall structure is acceptable.

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 adequately describes the return format as records with actions. It also covers side effects and input fallback behavior, though it does not mention error cases or permission requirements.

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?

The parameter descriptions add useful examples and explain client/domain behavior. However, the domain description says 'Uses the client's registered domain when omitted' even though the schema marks domain as required, creating a contradictory instruction.

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 clearly explains that the tool plans email setup by reading current records and returning proposed actions (create, update, merge, unchanged). It also distinguishes itself from apply_mail_setup, making its purpose unambiguous.

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 says to pair it with apply_mail_setup, which needs the plan id, and clarifies that it changes no DNS. It could be more explicit about using it as a dry-run before applying, but the guidance is still clear.

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