Check numbers on WhatsApp

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

Annotations already declare readOnlyHint=true, openWorldHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is fully covered. The description adds value by specifying that it returns contact id, business name, and username when known, and by noting it only reports numbers that have WhatsApp. 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 two sentences with no fluff. The core purpose is front-loaded, and the usage tip ('Check before sending to a new number') is a valuable addition. Every sentence earns its place; there is no redundancy.

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?

Despite having no output schema, the description explains the return content: contact id, business name, and username when known. Combined with the schema for inputs and annotations for safety, an agent has everything needed to invoke the tool correctly. The 'when known' phrasing appropriately signals that some fields may be absent.

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 input schema provides 100% description coverage for both parameters: phones (1-50 numbers, E.164 format) and accountId (the wuapi account id from list_accounts). The description does not add any parameter-specific meaning beyond the schema, so the baseline of 3 applies since the schema does the heavy lifting.

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 checks which phone numbers have WhatsApp and returns contact id, business name, and username when known. The verb 'check' is specific, the resource is 'phone numbers', and the outcome is unambiguous. It distinguishes itself from sibling tools like send_text or lookup_contacts by focusing on WhatsApp presence validation.

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 provides explicit usage context: 'Check before sending to a new number.' This implies the tool is used as a pre-send validation step, which is clear and actionable. However, it does not explicitly name alternative tools or state when not to use it, so it misses the exclusion clause that would earn a 5.

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