Verify a list of email addresses

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

The description adds substantial behavior beyond the annotations: it explains the send/hold/kill action taxonomy, the difference between DNS-tier and hosted-tier behavior, and the credit cost model. This is exactly the contextual information an agent needs to predict side effects and constraints.

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 compact and front-loaded with the key capacity limit, followed by the result shape and action meanings, then cost mechanics. Every sentence earns its place with no repetition or filler.

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?

Given no output schema, the description still covers the result shape, each action value, tier behavior, and cost implications. This is enough for an agent to select and call the tool correctly without additional lookup.

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 the baseline is 3. The description adds meaning by explaining what hosted probing entails, how free tier skips checks.smtp, and that max 500 addresses applies per call, enriching the semantic understanding beyond the raw schema.

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 and resource: 'Check up to 500 addresses in one call.' It clearly positions this as the batch variant of email verification, distinguishing it from the single-address sibling verify_email by the batch size and result format.

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 clearly communicates batch use with a 500-address limit, giving the agent context for when this tool is appropriate. It does not explicitly name verify_email or state when not to use it, so it falls just short of fully explicit alternative routing.

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