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

Annotations already declare readOnlyHint=false, destructiveHint=true, openWorldHint=false, but the description adds what those hints cannot: the write is confined to the caller's own record, it is undoable from the same surface, it executes immediately rather than staging, and it returns an ordinary result instead of a plan_token. That is genuinely decision-relevant context; the only soft spot is that it frames the action as reversible while annotations flag it destructive, which is a framing tension rather than an outright contradiction since the write is still disclosed.

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?

Front-loaded correctly: the verb, resource and id source come first. But the confirmation paragraph is dense policy prose that spends a sentence on 'plan_token' and a general rule about destructive/outbound/financial actions, only part of which the agent needs in order to invoke this specific tool.

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 tool this covers everything material: what it cancels, where the id comes from, that it fires without confirmation, that the effect is reversible, and what the response looks like. Nothing needed to call it correctly is missing.

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 coverage is 0% — reminder_id is a bare string with minLength 1 and no description — so the description must carry the meaning, and it does by naming the two tools that produce a valid id. It stops short of saying what happens on an unknown or foreign id.

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 and resource ('Cancel one of the caller's scheduled reminders') and pins the argument's provenance to two named sibling tools ('the id planner_set_reminder returned (or a reminder id from planner_get_agenda)'). That provenance implicitly separates it from the other cancel-style siblings (cancel_scheduled_notification, mail_cancel_scheduled) without opening their schemas.

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 activation condition — the caller asks for it — and an explicit boundary: destructive, outbound or financial work elsewhere must propose and wait. It does not name a concrete alternative tool for cases where this is the wrong choice, so the contrast is stated as a policy class rather than a sibling route.

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