Number Lookup

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

Annotations already cover read-only, idempotent, open-world, and non-destructive behavior. The description adds meaningful behavioral context by promising a fresh read of live numbering infrastructure and explicitly stating that carrier data is never cached, which is valuable beyond the annotations.

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 tight sentences with no filler. It front-loads the singular scope and core data domains, then adds the behavioral guarantee. Every clause earns its place, and it does not redundantly repeat the schema.

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 a full output schema, 100% parameter coverage, and annotations covering the tool's safety profile, the description supplies the remaining decision-relevant context: single-number live lookup and optional product selection. An agent has enough information to select and invoke this tool correctly.

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%, so both parameters are already fully documented in the input schema. The description adds only mild semantic context, such as clarifying that the lookup is for one number and that products are optional, which meets but does not exceed the baseline.

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 concrete read operation ('Live intelligence for ONE North American phone number') and enumerates the exact data domains returned: carrier, line type, LRN, porting activation, and optional CNAM, spam reputation, and messaging provider. The 'ONE' scope clearly distinguishes it from bulk siblings like vri_bulk_lookup.

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 gives clear context: use this for a single number where you need fresh carrier/routing intelligence and optionally additional data products. It does not explicitly name alternatives or state when not to use it, but the emphasis on 'ONE' and the later 'never cached' guarantee imply the boundaries against bulk and stale-data tools.

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