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

Annotations already declare destructiveHint=true, idempotentHint=false, readOnlyHint=false, so destruction is known. The description adds genuine context beyond them: approval gating before credit use, the non-deletability of designs in active campaigns, and the fact that writes are never auto-retried. It does not describe effects on recipients/campaigns or reversal, but it substantially supplements the annotations.

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 critical approval constraint is buried behind a duplicated first sentence. 'Delete design. Delete a design.' is pure waste, and the useful content (campaign block, approval gate, no-retry notice) follows in a compressed stream without structure.

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 destructive mutation with annotation coverage and no output schema, the definition covers the main agent risks: approval gating, credit use, the active-campaign restriction, and automatic retry behavior. Missing only the failure/error outcomes for a blocked delete or the state of the design afterwards, which are minor for this tool.

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?

With 50% schema coverage, the description only restates that confirmed=true is required, which the schema already says, and says nothing about the nested path.id 'Resource ID' beyond what the schema provides. It adds no syntax, format, or meaning that the schema does not already convey, so the baseline 3 is appropriate.

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 verb+resource is technically present, but the opening two sentences ('Delete design. Delete a design.') are a verbatim restatement of the title and tool name, adding no information about which entity is deleted or its scope. It never mentions the mail-design concept or distinguishes the operation from the patch/get mail_designs siblings that share the resource.

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?

'Designs used in active campaigns cannot be deleted' is an explicit when-not condition, and 'Requires user approval and confirmed=true' is a stated prerequisite. No comparison to update/retrieve alternatives is offered, but the exclusion condition is clear and actionable.

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