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

Rich disclosure well beyond what the annotations provide: today sets status Cancelled with immediate access loss, a future date sets Pending Cancel with access retained, plus billing-avoidance advice, a confirmation-default note, and the API key requirement. None of this is in the readOnly/destructive/openWorld hints.

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-loads the core action and the two timing outcomes before secondary billing and auth notes. Slightly redundant: the per-call confirmation is stated twice ('By default you confirm each call' and 'confirm with the user before each call').

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 mutation tool with no output schema, the description covers outcome semantics, timing effects, billing implications, confirmation policy, and auth needs. Nothing an agent needs to invoke it safely 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 100% (baseline 3), but the description adds real semantic value for cancel_on by explaining what 'today' versus a future date actually does to status and access, which the schema's 'Default: today' does not convey.

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 (Cancel) and resource (a member's plan), and its clause 'now or on a future date' distinguishes it from siblings like pause_member_plan and switch_member_plan. An agent can identify the operation 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 clear context on the two timing modes and even prescribes when to schedule the date (one day before the next bill date). It stops short of naming the actual sibling alternatives (pause_member_plan, switch_member_plan), so routing between sibling cancellation-adjacent tools is left partly to inference.

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