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

With no annotations, the description carries the full burden. It discloses the cost (3.00 USDC) and payment method (x402 per-action), which are important behavioral traits. However, it does not explain the payment flow (e.g., initial call without payment), eventual number lifecycle, or any other side effects.

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, front-loaded with the main action and cost. Every word contributes, with no fluff or repetition.

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?

The tool involves a payment flow (schema notes 'omit on first call to receive payment instructions') and no output schema, but the description omits this procedural detail and does not indicate what the response contains. For a 3-parameter purchase tool with no annotations, this is inadequate.

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 covers country and payment with descriptions, but areaCode lacks a description. The tool description does not add any parameter-level meaning, failing to compensate for the missing areaCode semantics. Schema coverage is 67%, but the description provides no additional value.

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 ('Provision') and resource ('real phone number (SMS + voice)'), clearly distinguishing it from temporary number sibling tools like phone_temp_number. It also states the purpose ('for your agent') and adds cost context.

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 implies usage for a real, paid, likely permanent number ('real phone number' and cost), but does not explicitly mention when to use this tool versus alternatives such as phone_temp_number. There is no when-not-to-use guidance, leaving usage to be inferred.

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