Validate Phone Number

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

With no annotations, the description carries the behavioral burden. It discloses normalization behavior (accepts spaces, dashes, parentheses, optional country code), what it returns (validity, E.164, national format, line type), and even highlights tricky regional cases. It doesn't mention error handling or side effects, but validation terminology implies a read-only operation.

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 dense but every part earns its place: the core verb, supported countries, input flexibility, return fields, tricky cases, and ideal use cases are all packed into a compact block. No filler or redundant phrasing.

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 there is an output schema, the description doesn't need to detail return values. It provides enough information to call the tool correctly: supported countries, input format tolerance, and the distinguishing regional complexities. Missing error behavior is a minor gap for a validation tool.

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 0%, so the description must compensate. It fully explains 'country' as an ISO 3166-1 alpha-2 code with the 15 supported values, and clarifies that 'number' can include or omit country codes and accept various formatting characters. This adds significant meaning beyond the bare parameter names.

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 normalize') with a clear resource ('Latin American phone number'). It distinguishes itself from sibling validation tools (validate_pix_key, validate_tax_id, validate_bank_account) by being phone-specific and listing supported countries and normalization behavior.

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 for when to use the tool: 'Ideal for WhatsApp, SMS/OTP and CRM hygiene.' It doesn't explicitly state when not to use it or name alternative tools, but the supported country list and use cases make selection straightforward.

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