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

The description supplies genuinely useful behavior (nothing further is charged, refund path, access kept until keeps_until, monthly card subscription stops, pointer to account.cancel.losses). However, it also states the user must accept losing what the plan added, which conflicts with the declared destructiveHint=false and with the schema's own 'losing what the plan added' wording — an agent trusting the annotation would underestimate risk.

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 with the key action, but the refund rule is stated twice in near-identical wording ('a purchase under 7 days and a paid period that has not started are refunded and end now' vs the later restatement), and the literal JSON example duplicates the schema. Roughly half the text is 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?

No output schema exists, and the description compensates by naming the keeps_until field and pointing to account.cancel.losses in GET /api/plans for the losses detail, plus the out-of-band refund route. Only the immediate response shape is unaddressed.

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 single parameter already documents that it must be true and what accepting it means. The description only restates this and shows a literal payload example, adding no semantics 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 'Cancel the active plan' gives a specific verb and resource, which is easily separable from siblings like buy_plan, list_plans, and billing. It does not explicitly name those siblings, but the action is unambiguous.

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?

It states the precondition (requires accept_data_removal: true), the effect window (refunded if under 7 days or unpaid period), and routes USDC/credit-paid purchases out of the tool toward e-mail refund. Missing an explicit 'use buy_plan instead if...' contrast, but usage context is clear.

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