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

Annotations already cover the safety profile (readOnly, non-destructive, closed-world), so the description focuses on behavior the agent could not otherwise know: one row per address, provider attribution per row, per-row credit cost, and that 'unknown' rows are not billed. That billing detail is genuinely useful context beyond annotations, though pagination behavior is not described.

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 return shape is front-loaded in the first clause, and each sentence adds information about verdicts, per-provider attribution, credits, and filtering. Some parenthetical explanation (catchall_validated, unknown) is dense but earns its place by disambiguating enum values.

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 must convey the return shape, and it does: rows keyed by address, verdict field, provider-level responses, and credit cost per row. Filtering and result semantics are covered, and pagination is fully documented in the schema, so nothing an agent needs to call this correctly is missing.

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 schema baseline is 3. The description goes further by defining the semantics of the composite 'deliverable' enum value ('valid plus catch-all'), which the schema only names; that added meaning is exactly what a description should contribute.

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 states a concrete return shape: 'Returns one row per address with its verdict' along with the enumerated verdict values. That is a specific verb-plus-resource. It stops short of distinguishing itself from nearby siblings like get_email_verification_rates, so it is clear but lacks explicit sibling differentiation.

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 guidance is limited to the filter parameter: it explains that 'deliverable' means valid plus catch-all and is what a campaign actually sends to. There is no explicit statement of when to choose this tool over get_email_verification_job or get_email_verification_rates, so the when-to-use context is implied rather than stated.

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