verify_emails

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

The description adds meaningful details beyond the read-only, idempotent, and non-destructive annotations: it consumes verification credits per address, requires an API key, returns 'undeliverable' as a successful result, and confirms nothing is sent to addresses. There is no contradiction with the annotations.

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 appropriately sized and front-loaded with the core purpose, then expands into timing, usage constraints, cost, auth, and output semantics. Every sentence contributes distinct information, with no redundant fluff.

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?

Despite having no output schema, the description explains what the return value is (a deliverability verdict per address) and the key semantic nuance that 'undeliverable' is still a successful result, not an error. Together with API-key and credit-cost information, the tool is fully usable by an agent.

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?

The input schema already documents both parameters fully, so this is at baseline 3. The description adds extra semantic value by clarifying that only one parameter should be used and that a batch of 20 costs 20 credits, which makes the `emails`-billing relationship 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 opens with a specific action and resource: checking whether email addresses are deliverable. It also states the one-at-a-time versus up-to-20-at-a-time scope, which clearly differentiates it from other lead/deal/send tools in the sibling list.

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 explicitly says when to use this tool ('Run this before a send to protect sender reputation') and gives the parameter usage rule ('Pass either email for one or emails for a batch, not both'). It does not explicitly name alternative tools or when-not-to-use cases, but the context is clear.

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