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

Adds real value beyond annotations: one credit consumed per address (a cost signal), one result per address, and the tri-state meaning of "unknown". Gaps remain on partial-failure behavior (does one bad address fail the whole batch?) and any rate/auth constraints, which matter for a non-idempotent, open-world tool.

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?

Three tightly packed sentences: capability and cost first, then return shape, then the escalation rule. Zero filler and the most decision-relevant constraint (size limit → sibling tool) is not buried.

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 still explains the return contract (one result per address, same fields as verify_email, "unknown" semantics), and it covers the cost and routing model. An agent can call this correctly and knows what to do with oversized inputs.

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% and the single parameter already documents the 1-to-20 range and item constraints, so the schema carries the burden. The description only restates the batch bound and adds that results align one-per-address, which is marginal over the schema.

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 and resource (verify email addresses), the batch size bound (1 to 20), and names the provider. It is clearly distinguishable from verify_email (single) and create_bulk_job (large batches/files) without opening either schema.

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?

Explicitly routes the agent: use create_bulk_job for 21+ addresses or any attached file, and an explicit prohibition against splitting a large list across multiple calls. Both the when and the when-not are stated with the alternative named.

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