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

With no annotations, the description carries the full burden. It discloses all verification checks (syntax, domain mail exchanger, disposable, role, typo) and normalization, and explicitly states the absence of SMTP probing. It does not cover authentication needs or rate limits, but provides sufficient behavioral details.

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 informative but slightly verbose. It front-loads the main purpose and then explains the rationale. Every sentence adds value, though some trimming could improve conciseness.

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 3 parameters, no output schema, and no annotations, the description provides a good level of context about what the tool does and its methodology. It lacks details on output format and error handling, but is reasonably complete for a verification 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 description coverage is low (33%), so the description must compensate. It explains the 'email' parameter by detailing the checks performed, but does not explicitly link the boolean parameters 'rejectRoleAccounts' and 'rejectFreeProviders' to their functions, though 'role-account detection' and 'disposable service' are mentioned. Adds some value but could be more explicit.

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 specifies a clear verb ('checks') and resource ('e-mail address'), and lists multiple verification aspects (syntax, domain mail receipt, disposable detection, role detection, typo correction, normalization). It distinguishes itself from competitors by explicitly stating what is not done (no SMTP probing).

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 explains what the tool does and does not do, and provides reasoning for its approach. It implicitly suggests when to use it (when reliable verification without SMTP probing is needed) but does not explicitly mention alternative sibling tools or when not to use it.

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