Send SMS — NANP / North America (Telnyx)

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

Annotations already indicate readOnlyHint=false and destructiveHint=false, so the description adds useful behavioral details like pricing per message and the specific error code for invalid destinations. However, it does not mention potential billing charges beyond the per-message cost or rate limits, but given the annotations, the description adds some context.

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 very concise: three short sentences, front-loaded with the action and key scope. Every sentence adds value with no redundancy, making it easy to parse quickly.

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 has an output schema (not shown) so return value documentation is not required. The description covers purpose, pricing, error condition, and a related tool. It does not discuss authentication or prerequisites, but the schema for 'from' parameter includes that context. Overall, the description is sufficiently complete given the support from schema and annotations.

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% and each parameter is well-documented with format and constraints. The description does not add new parameter-specific semantics beyond what the schema provides, achieving the baseline score.

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 action ('Send SMS') and delineates the geographic scope ('North America — NANP +1 — US, Canada, Caribbean'). It also includes pricing, the cheapest tier, which distinguishes it from other SMS tools like sms_premium or sms_world.

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 explicit usage guidance by suggesting to use telnyx.estimate_price first if uncertain about the destination, and notes that a 400 error will occur if the destination is outside +1. This helps an agent decide when to use this tool versus alternatives.

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