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

Annotations already declare readOnly, idempotent, openWorld, and non-destructive, so the safety profile is covered. The description adds genuinely new context beyond that: the credit cost ('Spends 1 credit per item'), which is a material behavioral trait an agent cannot infer from structured fields.

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, no filler, with the batch scope and cost front-loaded. Every sentence carries distinct information (scale, return shape, billing).

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?

With an output schema present, the return format needn't be described, and the description still adds scale limits and cost. It leaves unaddressed what happens on partial validation failures or oversized input, which would round out a bulk mutation-adjacent tool operating on external data.

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% and the enum for 'type' is fully documented in the schema, so the baseline is 3. The description's 'up to 50' merely restates the schema's maxItems constraint and adds no format or semantic detail beyond it.

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 (validate) and resource (phones, emails, IPs) plus a concrete batch scope ('up to 50 ... in one call'), which separates it from single-item siblings like validate_phone and verify_email. It stops short of naming those siblings explicitly, so the differentiation is inferable rather than spelled out.

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 phrase 'in one call' implies this is the efficient choice for multiple values, which is a mild usage signal. However, there is no explicit when-to-use vs when-to-use-a-single validator guidance and no stated exclusions or prerequisites.

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