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

With no annotations, the description carries the full burden and does well: it discloses that each call costs 1 Fox Credit, that a repeat within 24 hours is answered from a result cache yet still billed, and that the return includes a 0-100 quality score. It does not cover auth/prerequisite requirements or failure/timeout behavior, which keeps it short of full transparency.

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: purpose, method, and return shape come first, then the billing and cache caveat. Every sentence earns its place and the cost caveat is front-loaded enough to matter before invocation.

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, and the description compensates by stating the return is a 0-100 quality score, plus the billing and cache semantics an agent needs before calling. Missing details are error handling and what the score thresholds mean, but the essentials are covered for a two-parameter tool.

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 (email and proxy) are already documented in the schema. The description adds nothing parameter-specific beyond stressing a single address, so it neither helps nor harms relative to the baseline 3.

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 names a specific verb (verify) and resource (ONE email address) and enumerates exactly what is checked (syntax, MX, SMTP, catch-all, disposable, free-provider, role). The capitalized 'ONE' signals the single-address scope and implicitly contrasts with the plural sibling verify_emails, though no sibling is named outright.

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?

Usage context is implied by 'ONE email address' and the per-check credit price, which suggests this is the single-address path while verify_emails handles batches. However, the description never explicitly says when to prefer a sibling or when not to use this tool, leaving the routing to inference.

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