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

With no annotations provided, the description carries the full burden and does so well: it discloses the verification checks, the valid/risky/invalid verdict with score, the absence of SMTP probing and sending, the batch limit, runtime, and pricing. These are exactly the behavioral details an agent needs before invoking it.

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 dense but front-loaded: the core purpose comes first, followed by the checks performed, verdict model, operational caveats, and pricing. Nearly every phrase carries useful information for selection or invocation.

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 the simple one-parameter schema, lack of annotations, and no output schema, the description is complete: it explains what is checked, what verdict is returned, what is not done (SMTP/mail), and the cost. There is no material gap for an agent deciding whether and how to call it.

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 input schema has 100% description coverage and already documents that the parameter accepts 1-20 comma-separated emails. The description repeats the 20-address cap but adds no meaningful syntax or formatting detail beyond the schema baseline.

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 gives a specific verb and resource ("Email verification / validation API") and enumerates exactly what is checked: syntax, MX, provider, disposable domains, free webmail, role accounts, typo suggestions, and verdicts. This makes it clearly distinguishable from sibling tools such as company_enrich or prompt_injection_check.

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?

It establishes a use context for lead lists and states the per-call limit and runtime, but does not explicitly say when to choose this tool over alternatives or when not to use it. The usage is implied rather than framed as explicit decision guidance.

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