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

With no annotations, the description carries the full behavioral burden. It usefully discloses a cost of 1 credit, which is a genuine behavioral trait absent from the schema, but it omits whether verification is a passive lookup or an active SMTP probe, whether it sends anything to the address, and how reliable catch-all detection is. Partial disclosure only.

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?

Two short sentences, front-loaded with the core capability and followed by the cost constraint. Every sentence carries information; nothing is padding.

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?

There is no output schema, but the description enumerates the possible verdicts (deliverable, catch-all, disposable), effectively sketching the return values, and the credit cost is stated. For a single-parameter, no-annotation tool this is nearly sufficient, though accuracy/latency expectations remain unstated.

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 single parameter has 100% schema description coverage ('Email to verify'), so the schema already documents it fully. The description adds no syntax, format, or normalization guidance beyond what the schema provides, which is the expected baseline.

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 gives a specific verb (Check) and resource (email) plus the exact result categories it distinguishes: deliverable, catch-all, disposable. That is far more informative than a tautological restatement. It doesn't explicitly differentiate itself from the sibling 'emails' tool, so it falls short of a 5.

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?

There is no guidance on when to reach for this tool versus alternatives like 'emails' or 'profiles', and no prerequisites or exclusions are stated. Usage is only implied by the tool's name and stated outcome categories.

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