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

It goes beyond the readOnly/destructive annotations by disclosing a material operational cost: 'Spends 1 credit per item.' It also notes the per-item result array, which is useful behavioral context even though an output schema exists.

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 short sentences deliver the core capability, the batch limit, the return shape, and the cost in order of importance. There is no redundant or filler content.

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?

For a simple batch-validation tool, the definition covers what it does, the limit, the result shape, and the credit cost. The annotations and output schema fill in safety and return details; the only notable omission is explicit guidance on when to prefer single-item siblings.

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 input schema already documents both parameters, including the enum values and maxItems. The description adds little beyond restating the resource types and batch size, so a baseline score of 3 is appropriate.

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 states a specific verb ('Validate') with concrete resources (phones, emails, IPs) and a clear batch constraint (up to 50 in one call). This distinguishes it from single-item sibling tools like validate_phone and verify_email.

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 clearly implies bulk usage by saying 'in one call' and 'up to 50,' which helps an agent choose it over repeated single validations. However, it does not explicitly name alternative single-item tools or state when not to use it.

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