sms_rental_order

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

With no annotations, the description carries the full burden. It usefully discloses the paid nature and exact cost ('18 USDC on Base via x402'), which is real behavioral context beyond the schema. It omits other behavior: whether a number is guaranteed, what happens on failure, auth needs, and how message reading relates to sms_rental_messages.

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?

A single front-loaded sentence with zero waste. The action, scope, and cost are all packed efficiently into one line. Every clause earns its place.

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 paid mutation tool with no annotations and no output schema, the description covers the cost and payment rail but not the return shape (rental id? phone number?). Its 'read every SMS' phrasing overlaps ambiguously with the sms_rental_messages sibling, leaving the agent unclear on whether reading is bundled or a separate call.

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 are fully documented in the schema, establishing the baseline of 3. The description's '1 or 7 days' merely restates the enum already in the schema and adds no new syntax or constraints. It says nothing about confirmNewPurchase.

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?

Specific verb+resource+scope: 'Rent a US phone number for 1 or 7 days and read every SMS it receives.' An agent knows exactly what it does. However, it does not distinguish itself from sibling tools like sms_rental_quote, sms_order, or sms_rental_messages, which the description's SMS-reading claim overlaps with.

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?

No when-to-use guidance and no mention of alternatives such as sms_rental_quote (get a price first) or sms_rental_messages (read messages). The '(paid)' hint implies a purchase, but there is no explicit routing logic. Nothing tells the agent when this is the right call versus its siblings.

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