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

With no annotations, the description carries the full behavioral burden. It usefully discloses that `registered: false` is normal, not an error, and states the billing cost of 1 credit per call. It does not cover auth requirements, rate limits, or the full response shape, so it remains only minimally sufficient.

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 short, front-loaded, and wastes no words. The core purpose comes first, followed by a critical interpretation note, group label, and billing detail. Each sentence contributes useful context.

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?

For a one-parameter check with no output schema and no annotations, the description gives an adequate picture: what is checked, what the result means, and the billing cost. It could more fully specify the response format or any auth/rate-limit constraints, but the essential invocation context is present.

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%, and the single `phone` parameter already has a detailed format description. The tool description adds no additional parameter semantics beyond what the schema provides, so the baseline of 3 applies.

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 specific verb-resource pair: checking whether a phone number has a WhatsApp account and retrieving its WhatsApp id. It is clear and concrete. However, it does not explicitly differentiate the tool from its sibling get_v1_number_profile, leaving the agent to infer the distinction.

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?

Usage is implied by the purpose, and the note that an unregistered number is a normal answer rather than an error is helpful interpretation guidance. Still, there is no explicit when-to-use condition, no prerequisite, and no named alternative such as get_v1_number_profile.

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