Phone Lookup

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

Annotations already declare readOnlyHint, openWorldHint, idempotentHint, and destructiveHint. The description adds significant value by specifying rate limits (30/hr free, 500/hr pro) and a critical behavioral trait: the carrier field is omitted for certain regions and carrier_status must be interpreted accordingly. This prevents incorrect inferences by the agent.

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 with purpose first, then format requirements, companion tools, rate limits, and return behavior. It is concise but slightly redundant with the schema examples. Every sentence contributes, but it could be more streamlined.

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 output schema exists, the description sufficiently explains return values and adds crucial behavioral context about carrier omission and carrier_status interpretation. It covers edge cases (MNP-restricted regions) and rate limits, making it complete for an agent to use 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 coverage is 100% with a detailed parameter description including format examples. The description reinforces the E.164 format but does not add new semantic meaning beyond the schema. Baseline is 3 for high coverage.

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 uses a specific verb 'Validate and analyze' and clearly lists expected outputs (country, region, carrier, line_type, timezone, formats). It distinguishes itself from siblings by mentioning companion tools username_lookup and email_disposable for identity investigation, making its role in the toolkit clear.

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 explicitly states when to use the tool: to verify phone legitimacy and detect fraud risks. It mentions companion OSINT tools for identity investigation, providing context. However, it lacks explicit 'when not to use' guidance or alternatives besides the companions, which would prevent misuse.

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