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

Annotations already declare the operation read-only, idempotent, and non-destructive. The description adds critical behavioral and cost context beyond annotations: 'Each number is a fresh paid read — spend scope required.' This is exactly the extra information an agent needs before invoking a potentially expensive call.

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 two sentences with no filler. The core capacity and geographic scope are front-loaded, followed by the product list and the essential cost caveat.

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?

The description provides the max batch size, the number types and formats accepted (schema), the optional products, and the spend authorization requirement. With an output schema available, nothing needed for correct invocation is missing.

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 schema already covers both parameters at 100%, so the baseline is 3. The description adds value by mapping the lrn product to 'carrier, line type, routing' and labeling cnam/spam/messaging as optional, which helps an agent choose products without external domain knowledge.

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 and resource: a live lookup for up to 100 North American phone numbers in one call. It also lists the data types returned (carrier, line type, routing; optional cnam/spam/messaging), which clearly distinguishes it from a single-number lookup tool.

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 'up to 100 North American phone numbers in one call' provides clear context for when to use this bulk tool. It does not explicitly name vri_number_lookup as the single-number alternative or state when not to use it, but the batch semantics are obvious enough.

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