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

Annotations already carry readOnlyHint and openWorldHint, so safety is covered. The description adds genuinely useful behavior beyond that: the negative guarantee that no SMTP probing occurs and mailbox existence is unverified, plus the discrete verdict vocabulary. It does not discuss rate limits or DNS lookup failure modes.

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?

Front-loaded with purpose, then the check list, then the return contract, then the key limitation. Dense and mostly functional, though the long enumeration sentence could be tightened; every clause still carries information.

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?

No output schema exists, so the description carries the return-value burden and does so by naming all four verdicts and the score range. Combined with the explicit non-coverage of SMTP probing, an agent has everything needed to call and interpret 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 description coverage is 100% and there is a single required 'email' parameter, so the schema fully documents input semantics. The description adds no format details (single address vs list, normalization) beyond the schema, so baseline 3 applies.

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?

States a specific verb (verify) and resource (email address) and enumerates exactly which checks run: syntax, disposable-domain, role-account, free-provider flag, typo suggestion, and DNS MX/A. The return contract (valid/risky/invalid/unknown plus 0-100 score) is specified, so an agent knows precisely what this tool produces.

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?

Frames the intended context ('AI agents and lead-qualification pipelines') and explicitly rules out an important alternative method: 'No SMTP probing, so mailbox existence is not confirmed.' That exclusion tells the agent when this tool is insufficient. It stops short of naming a sibling or stating when to prefer e.g. email_auth for SPF/DKIM/DMARC, so no explicit alternative routing.

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