Search phone numbers to buy (by country)

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

Annotations are absent, so the description must carry the full behavioral burden. 'List' implies a read-only operation, which is helpful, but it does not disclose the output format (fields like phone number, price, or availability), pagination, rate limits, or any authentication requirements. The downstream usage adds context but does not compensate for the missing behavioral details.

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?

Two sentences with zero waste. The first sentence states the action and purpose; the second gives concrete next-step guidance. Every sentence earns its place, and the structure is front-loaded with the primary purpose.

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 tool's low complexity (2 params, 1 required) and full schema coverage, the description provides enough context: it names the source (Twilio), the purpose, and how to use the result. It does not describe the output fields (e.g., whether the list includes pricing), but this is reasonably inferable for a listing tool. Overall, it is sufficiently complete for an agent to call it correctly.

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%, so both parameters (countryCode and numberType) are already fully described in the schema. The description adds no extra meaning for the parameters themselves; it only explains how the output is consumed. Thus the baseline of 3 is appropriate.

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 ('List'), a clear resource ('phone numbers available to purchase'), and the purpose ('so you can pick one to buy as the account's SIM/number'). It clearly differentiates from the many create/update siblings by focusing on the search step, and it even names the downstream tools that consume the result.

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?

It provides clear usage context: use this tool when you need to find a phone number to purchase for an account. It gives explicit downstream instructions (pass the chosen phoneNumber to gambot_create_trial_account/gambot_create_paid_account with simInfo.selectedSimNumber and purchaseInTwilio=true). It does not explicitly mention alternatives, but no direct alternative exists among siblings, so this is adequate.

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