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

Annotations only declare destructiveHint=true; the description adds that it is a WRITE, that the action cannot be undone, and that the server enforces the SCHEDULED-status precondition by refusing already-sent messages. That enforced-refusal behavior is genuine context beyond the annotation, though no auth or rate-limit details are given.

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?

Dense but front-loaded: the WRITE marker and core action lead, preconditions follow, the irreversibility warning is explicit, and the endpoint tag closes. No sentence is padding.

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, no-output-schema cancellation tool, the description covers the precondition, the irreversibility, and the failure mode. It does not state what the call returns, but with no output schema and a DELETE-style operation that gap is slight.

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 message_id field already documents its source (smsmode_send_sms or smsmode_list_messages), so the description need not repeat format details. It adds no parameter meaning beyond the schema, which is the expected baseline here.

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 (cancels) and resource (ONE scheduled message), plus the precise status precondition (SCHEDULED, sent with send_at) that distinguishes it from any read/list sibling. An agent can select it without opening the schema.

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?

Gives a clear when-to-use condition (message still scheduled via send_at) and a when-not condition (smsmode refuses messages already sent). It does not name a sibling alternative, but no other sibling performs cancellation, so the omission is minor.

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