phone_system_purchase_phone_number

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

Annotations already indicate readOnlyHint=false (mutation) and idempotentHint=false, which the description implicitly agrees with by saying 'purchase'. However, the description adds no extra behavioral context such as billing implications, compliance requirements, or consequences of repeated calls. It does not contradict annotations, but it doesn't enrich them beyond the basic mutation implication.

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 a single, concise sentence with no wasted words. It is front-loaded and easy to parse. However, it is arguably too terse for a tool with 10 parameters and compliance aspects, so it could benefit from a slightly expanded structure. Still, it earns a 4 for being direct and clear.

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 complexity (10 parameters, regulatory SIDs, KYC flags) and lack of output schema, the description is far too minimal. It doesn't mention what the tool returns, prerequisites like compliance documents, or common pitfalls (e.g., number unavailability). The annotations provide no additional context. An agent cannot fully understand the tool's behavior from this description alone.

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 all 10 parameters are documented in the schema. The description adds no additional meaning to the parameters. With full coverage, the baseline is 3, and since the description offers no extra clarification or grouping, it stays at baseline.

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 the specific verb 'purchase' and the resource 'phone number', clearly stating the tool's action. It distinguishes from siblings like phone_system_available_numbers (which lists purchasable numbers) and phone_system_active_numbers (which lists current numbers) by implying the purchase action, though it doesn't explicitly mention those distinctions. The purpose is unambiguous.

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 no guidance on when to use this tool versus alternatives like phone_system_available_numbers or phone_system_active_numbers. There is no mention of prerequisites, conditions, or exclusions. An agent would have to infer from the tool name and siblings. This is a clear gap for a 10-parameter tool with regulatory implications.

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