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

Beyond the annotations, the description reveals that the check is two-stage, includes catch-all analysis, returns specific statuses, and costs credits per call. It aligns with destructiveHint: true by explaining the cost side effect, and with readOnlyHint: false by implying an operation with consequences.

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 focused sentences contain the core purpose, the key behavioral nuance (catch-all analysis), the return statuses, and the cost implication. There is no filler or repetition of schema details.

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, listing the exact statuses is valuable and nearly sufficient for the agent to interpret results. The cost warning and catch-all detail round out the practical context, though usage guidance remains absent.

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 schema documents idempotency_key well but leaves email undocumented; the description adds no parameter-level detail. However, 'one email address' implicitly ties to the email parameteraine, and the email parameter is self-explanatory by name.

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 ('deliverability of one email address'), then adds distinctive detail (two-stage check, catch-all analysis) and enumerates the possible statuses. Even without naming a sibling, this clearly distinguishes the tool from the unrelated campaign/lead/enrichment siblings.

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?

No guidance is given about when to choose this tool over alternatives, nor does it state prerequisites or contexts where email verification is appropriate. There are no sibling verification tools, but the description still leaves the agent to infer when to call it.

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