phone_lookup

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

Annotations indicate read-only, non-destructive, idempotent behavior. The description adds beyond annotations by noting that carrier is omitted from the wire in MNP-restricted regions and instructs to always check carrier_status. No contradictions with 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 well-structured with front-loaded purpose, then usage guidelines, tier limits, and return details. It is concise but includes necessary behavioral notes. Every sentence adds value.

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 low parameter count, complete schema coverage, and presence of an output schema (mentioned), the description is fully complete. It covers input format, special cases (carrier omission), and return fields, leaving no ambiguity.

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 single parameter described with examples and formatting guidance. The description adds value by providing correct and incorrect format examples, helping agents use the tool correctly.

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 clearly states the tool validates and analyzes phone numbers, returning country, region, carrier, line type, timezone, and formatted versions. It distinguishes itself from sibling OSINT tools like username_lookup and email_disposable by focusing on phone number verification and fraud detection.

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 says to use for verifying phone legitimacy and detecting fraud risks. It provides format requirements (E.164) and mentions companion tools, giving context for when to use this tool versus alternatives. However, it doesn't explicitly 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.