rent_number

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

With no annotations provided, the description carries the transparency burden. It discloses an important behavioral aspect: quote-then-commit pricing, ensuring 'you never pay above what you saw.' This adds meaningful context beyond the schema. However, it does not mention potential side effects or return behavior, but the pricing guarantee is significant.

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 three concise sentences, each serving a purpose: stating the main action, explaining kinds, and providing an alternative plus pricing behavior. It is front-loaded with the core purpose and avoids unnecessary filler.

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 description covers purpose, kinds, alternative, and pricing behavior, but lacks information about return values or error conditions. Since there's no output schema, the agent is left guessing what the response contains. The mention of max_price_cents not in the schema also creates a completeness gap, making it less reliable for full invocation.

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 description adds value by explaining the 'kind' parameter values (verification: single SMS/20min; rental: timed LTR) and implies duration usage. However, it references 'max_price_cents' which is not present in the input schema, creating confusion for an agent attempting to invoke the parameter. Schema already covers duration and service_id, so the description's net contribution is mixed.

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's purpose: 'Rent a US non-VoIP phone number.' It immediately distinguishes between two kinds ('verification' vs 'rental') with specific meanings, and explicitly contrasts with purchase_dedicated_number for a different use case, making it distinct from siblings.

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 clear usage guidance: 'For a private all-services monthly number, use purchase_dedicated_number instead' gives an explicit alternative. It also explains when to use each kind (verification for single SMS/20min, rental for timed LTR), but could be more explicit about other exclusions. Overall, it gives solid context for tool selection.

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