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

Annotations already declare destructiveHint=true and readOnlyHint=false, so the safety profile is covered. The description adds the non-obvious behavioral guard that this only works while the message is still pending, which is real value beyond the annotations. It doesn't state what happens on an already-sent id (error? silent no-op?), keeping it below 5.

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?

A single sentence with no filler, front-loading the action and immediately qualifying the precondition and the id source. Nothing redundant.

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 two-parameter mutation with no output schema, the description plus rich schema docs cover what an agent needs: the precondition, the required id and its provenance, and the admin-only scope. Only the outcome of a failed cancel (already sent / unknown id) is left unstated.

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%, so both parameters are already documented, including the admin-only restriction on target_user_id. The description only adds provenance for 'id' (which sibling produces it), which is modest added value over the schema — baseline 3 applies.

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 ('Cancela') and resource ('mensagem agendada') plus the key precondition that the message has not yet been sent. That distinguishes it from delete_* siblings in the toolset, though it does not explicitly name an alternative cancel path.

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 clear usage context: only messages that haven't gone out, and it names the two siblings that supply the required id (list_scheduled_messages, schedule_whatsapp_message). No explicit 'do not use when already sent' fallback or error-handling guidance, so it falls short of a 5.

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