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

No annotations are provided, so the description fully carries the burden. It discloses the state requirement, the impossibility of unsending delivered messages, and the 404 error behavior for unknown or already-fired ids. This is strong behavioral coverage for a single-purpose tool.

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?

Three short sentences, each adding distinct value: what the tool does, when it works, and what error to expect. No filler or repetition.

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 one-parameter tool with no output schema, the description covers the operation, constraints, and error behavior well. It doesn't describe the success response, but that is a minor gap given the output is likely empty and the failure case is explicitly documented.

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 the single 'id' parameter is already documented as 'sms_messages row UUID'. The description adds no additional parameter semantics, but with complete schema coverage and one simple parameter, baseline 3 is appropriate.

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?

States a specific verb ('cancel') and resource ('scheduled SMS'), and clarifies the operation is for messages that haven't been sent yet. It is clearly distinct from siblings like sms_send_scheduled or 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?

Explicitly defines the valid condition ('status='scheduled'') and names an exclusion ('already-delivered messages can't be unsent'). It doesn't mention alternatives or how to find the id, but the condition alone gives sufficient usage context for a simple cancellation tool.

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