send_sms

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

With no annotations, the description carries the transparency burden. It discloses return values (message_id, message_sid, status, credits_charged) and explains optional parameter behavior (auto-assigned phone_number_id). However, it does not detail side effects like cost implications beyond credits_charged, delivery failures, or rate limits.

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 concise and well-structured: it opens with a one-line action, lists return values, then provides a clear Args list. Every sentence is informative, with no 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?

Given the tool's relative simplicity (3 params, output schema exists), the description covers the essential operation and parameter details. It could add edge cases or prerequisites (e.g., number provisioning), but the provided information is sufficient for most use cases.

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 input schema has no descriptions for parameters (0% coverage), but the description compensates fully with an Args section that explains each parameter including format (E.164), required/optional status, and auto-assignment behavior, adding meaning beyond the schema.

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 an SMS message') with a specific verb and resource. It distinguishes itself from siblings like send_email by naming the channel, making the 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 no guidance on when to use this tool versus alternatives (e.g., send_email, or other messaging tools). It does not mention prerequisites such as having a provisioned phone number or any exclusions.

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