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

Annotations declare this is not read-only, not idempotent, and open-world, so the agent already knows it has effects. The description adds meaningful context beyond that: the operation consumes credits from the connected BillionVerify account, which explains the cost/irreversibility implied by the non-idempotent hint. It does not quantify credit cost per address or note rate limits.

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 tight sentences with no filler. The core capability and the batch limit come first, and the chunking rule and credit note follow in order of operational importance.

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 does state the return shape at a high level ('a verdict for each'), which is what an agent needs to decide how to consume results. It stops short of describing possible verdict values or whether partial failures are possible across the batch.

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%, so both parameters (emails, check_smtp) are already documented in the schema. The description restates the 1-50 range that is already expressed via minItems/maxItems and says nothing about check_smtp or the SMTP trade-off, so it adds little beyond 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 (verify) and resource (email addresses), plus the batch limit and that a per-address verdict is returned. The batch framing implicitly distinguishes it from the sibling verify_single_email, though it never names that sibling explicitly.

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?

Provides actionable guidance for oversized inputs ('split longer lists into chunks of 50'), which is real usage instruction. However, it never says when to prefer this over verify_single_email or what to do if you only have one address, so routing between siblings is left to inference.

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