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

The description carries substantial disclosure beyond the annotations: nothing further is charged, the paid period remains active until keeps_until, and it points to `account.cancel.losses` in `GET /api/plans` to enumerate what is lost. It also distinguishes refund timelines by payment method, which the annotations do not cover. The one gap is that it never reconciles this irreversibility with `destructiveHint: false`, leaving the agent to reconcile a plan-ending, data-removing operation flagged as non-destructive.

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 core behavior is front-loaded in sentence one, which is good, but the remainder is a dense run-on mixing refund rules, timing, and payment-method exceptions without structure. The explicit JSON snippet in prose is partly redundant with the schema and costs space.

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?

With no output schema, the description correctly tells the agent where to inspect losses (`account.cancel.losses` via `GET /api/plans`) and what `keeps_until` signifies, which is enough to call the tool defensibly. Minor gap: it does not state whether the call is reversible or how to confirm success.

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 100% and the schema already states the parameter must be `true` and what it means. The description repeats the literal body `{ "accept_data_removal": true }` and reinforces that acceptance means losing what the plan added, but adds no syntax or edge-case detail beyond the schema.

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 opening sentence states a specific verb and resource ("Cancels the active plan") and immediately scopes the consequences. It is clearly distinguishable from siblings like list_plans, buy_plan, and reactivate_watches without needing to open 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?

The description gives rich conditional context (refund applies if purchased <7 days ago, or if the paid period hasn't started; USDC/credit purchases must be refunded by e-mail), which implies when the tool is appropriate. However it never explicitly routes the agent away from alternatives (e.g. buy_plan, reactivate_watches) or states a "when not to use" condition, so usage is only implied.

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