Verify an e-mail address

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

Annotations cover safety (readOnly, idempotent, non-destructive), and the description adds substantial behavior beyond that: the conditional SMTP/catch-all logic, the smtp_unreachable reason and null catch_all fallback, the tri-state validity output, the score, the typical latency, and the 1-credit cost. This is exactly the kind of context annotations cannot provide.

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 front-loaded with the checks performed and the return shape, packed into three dense but purposeful sentences. The parenthetical on SMTP fallback is slightly heavy but earns its place by explaining the null catch_all case.

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, the description appropriately explains the return values (validity, score, reason codes) and the fallback behavior. Cost and latency expectations are also disclosed. An agent has everything needed to decide whether and how to call 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?

Schema coverage is 100%, so the single parameter is already documented, and the 0-params baseline logic does not strictly apply. The description does not add syntax/format detail beyond the schema, but it enriches understanding by implying what gets evaluated against that input. Baseline 3-4 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 names the specific action (verifies an e-mail address) and enumerates exactly what is checked (syntax, disposable domain, role account, MX records, SMTP mailbox, catch-all). This is a precise verb+resource statement that clearly distinguishes it from the lead-search and provisioning 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?

Usage context is implied: you call this to validate an address before relying on it. However, the description offers no explicit when-to-use vs alternatives guidance and does not explain how this relates to the sibling tools (e.g. whether to verify before provisioning). Adequate but with a clear gap.

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