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

Adds substantial context beyond the annotations: per-call credit cost, the account-lockout risk of looping, and the underlying endpoint (POST /single/check). The credit spend is consistent with destructiveHint=true and readOnlyHint=false; nothing contradicts the annotation profile.

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?

Opens with the cost/effect warning, then purpose, then usage rules, then endpoint — front-loaded and dense. Every sentence (credit cost, loop prohibition, alternative tool) carries decision-relevant information.

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 response shape (result enum values, flags, suggested correction, optional parsed parts), so an agent knows what comes back. Cost, misuse risk, and the escape hatch for bulk work are all present.

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 coverage is 100%, so the baseline is 3; the description goes slightly beyond by explaining that address_info yields parsed address parts and contextualizing the outcome values. It does not add format guidance for timeout beyond the schema's 1-60 range, so it is a modest lift rather than a full one.

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 and resource ("Verifies ONE e-mail address") and enumerates the return surface (result values, flags, suggested correction, parsed parts). It also names the sibling it is not for (neverbounce_create_job for lists), so an agent can distinguish it from other neverbounce_* tools without opening schemas.

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 explicit when-to-use ("single address at the point of entry"), explicit when-not ("do NOT call it in a loop over a list or database"), the consequence (account lock), and the named alternative (neverbounce_create_job). This is the strongest form of routing guidance.

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