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

No annotations are provided, so the description carries the full burden of behavioral disclosure. It mentions the API source (2ip.me) and the return value format, but it lacks details on rate limits, authentication needs, error handling, or what 'valid' means (e.g., syntax check vs. deliverability). This leaves significant gaps for a tool that interacts with an external service.

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 well-structured and concise, with three sentences that efficiently cover the purpose, input, and output. Each sentence adds value: the first states the action and API, the second defines the parameter, and the third explains the return value. There is no wasted verbiage.

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?

Given the tool's low complexity (1 parameter, no output schema, no annotations), the description is moderately complete. It covers the basic purpose and return format but lacks behavioral details like error cases or API limitations. Without annotations or output schema, it should ideally include more about what 'valid' entails or usage constraints, leaving room for improvement.

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 description adds meaningful context beyond the input schema. The schema has 0% description coverage, but the description specifies that the 'email' parameter is 'The email address to verify,' clarifying its purpose. Since there's only one parameter, this adequately compensates for the low schema coverage, though it doesn't detail format constraints (e.g., valid email patterns).

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 clearly states the tool's purpose: 'Verify an email address using the 2ip.me API.' It specifies the verb ('verify') and resource ('email address'), though it doesn't differentiate from siblings since there are none. The description is specific but lacks the nuance of sibling differentiation that would warrant 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?

The description provides no guidance on when to use this tool versus alternatives. It states what the tool does but offers no context about prerequisites, limitations, or scenarios for its application. With no siblings, it could implicitly be the only option, but explicit usage guidelines are missing.

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