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

Annotations already cover readOnly and destructive hints, so the description adds meaningful behavioral context: the verification performs existence/deliverability checks and categories like disposable/role-based/risky. The 'Spends 1 credit' note adds cost behavior not present in 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?

Two concise sentences with no fluff. Every sentence contributes: functional scope and cost. The information is front-loaded and easily scannable.

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 simple single-parameter tool with an output schema and annotations covering safety, the description sufficiently covers behavior and cost. It is complete enough for an agent to select and invoke the tool correctly.

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 100% and the email parameter already has a clear description. The tool description reinforces the purpose of the parameter but does not add new format or constraints beyond what the schema provides. 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 description uses a specific verb ('Verify') and resource ('email address') and further defines the action: checks existence, deliverability, and flags disposable, role-based, and risky addresses. This clearly differentiates it from sibling tools like validate_phone and bulk_verify.

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 implies single-address verification and mentions 'Spends 1 credit,' hinting at a per-address cost versus bulk_verify, but it does not explicitly state when to use this tool over bulk_verify or other alternatives. No exclusions or alternative routing is given.

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