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

With no annotations provided, the description carries the full burden. It discloses critical behavioral traits: the cron dispatch mechanism, billing timing (debit at fire time), and the implication that a top-up before sending works. It does not mention cancellation or editing behavior, but the covered aspects are significant and useful.

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, with three sentences that front-load the core purpose and then add key constraints and billing behavior. It could be slightly more structured by separating the billing note, but it is efficient and well-ordered.

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 no annotations and no output schema, the description covers the essential details for correct invocation: future timestamp, billing timing, and dispatch mechanism. It lacks explicit mention of cancellation (handled by a sibling) but is generally complete for scheduling. The complexity is moderate, and the description fills the major gaps.

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 schema description coverage is 100%, so all parameters are already documented. The description adds value by clarifying that scheduledAt must be a future ISO 8601 timestamp, which reinforces the schema's example but does not add new semantics for other parameters. This is baseline credit per the rubric.

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: scheduling an SMS for future delivery. It specifies the verb 'schedule', the resource 'SMS message', and the key concept of future delivery, which distinguishes it from immediate send tools like sms_send_now and management tools like sms_cancel_scheduled and sms_list_scheduled.

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 context on when to use this tool (for future delivery) and implicitly contrasts with immediate sending via the billing comparison to 'send_now', but it does not explicitly state when not to use it or mention alternatives like sms_send_now or sms_cancel_scheduled by name. The context is clear but lacks explicit exclusions.

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