Send SMS — World (EU + APAC + LATAM core, Telnyx)

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

Annotations already indicate non-read-only, non-destructive, non-idempotent behavior. The description adds value by disclosing cost ($0.10/message) and error behavior for wrong destination regions, which are not in annotations. However, it does not detail response format or retry behavior, but output schema covers return values, so minor omission.

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 front-loaded with an action emoji and clear statement. Every sentence serves a purpose: listing countries, pricing, error conditions, and sibling tool references. No wasted words; concise yet comprehensive.

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 output schema exists (documenting return values), input schema is fully described, annotations are present, and sibling tools are distinguished, the description completes the picture with country lists, pricing, and error handling. No gaps remain for an agent to invoke 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?

Input schema has 100% description coverage, explaining each parameter. The description adds semantic context beyond schema by listing eligible countries and pricing, which helps agents understand where and at what cost the tool operates. The schema already covers format constraints and optional parameters.

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 verb 'Send SMS' and specifies the resource 'international destinations' with extensive country code examples. It explicitly distinguishes from sibling tools (sms_na and sms_premium) by naming error behavior, making purpose 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 explicit when-to-use guidance: it lists eligible country codes and states that errors indicate the wrong tier, directing to use sms_na or sms_premium. It also mentions pricing, giving a complete usage context.

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