email_verify

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

With no annotations, the description carries the full burden and does so: it states no email is sent (safety), that results are cached 6 hours, the exact cost ($0.0025 USDC) and p99 latency (15000ms). This is unusually rich behavioral disclosure that goes well beyond the structured fields.

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?

Dense but well front-loaded: purpose first, then statuses, then use cases, then operational facts (cache/cost/latency). Every clause carries information the agent needs, with only mild redundancy in the title-like opening.

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 compensates by enumerating the full return vocabulary (deliverable, undeliverable, catch_all, risky, unknown) with definitions for each. Cost, caching and latency round out everything an agent needs before calling.

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 the single 'email' parameter is already documented as 'Email address to verify.' The description's 'Params: email (required)' repeats the schema without adding format or syntax detail; baseline 3 is appropriate when the schema does the work.

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+resource ('checks whether an email address really exists') and the mechanism (SMTP RCPT TO probe), so the agent knows exactly what the call does. It does not explicitly differentiate from the sibling email_validate, which is the main ambiguity for selection.

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?

Gives concrete when-to-use contexts: 'before sending outreach, to clean lead lists or to block fake sign-ups.' However it names no alternative or exclusion, and the sibling email_validate is never mentioned, so the choice between the two 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.