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

Annotations only provide destructiveHint=true, so the description carries most of the load and does so well: it discloses that cancellation is deferred to period end and that the customer retains access until then. It omits whether the action is reversible/undoable and any permission or idempotency requirements, which keeps it short of a 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?

Three short sentences with zero filler; the critical behavioral fact (end-of-period, access retained) is front-loaded and the API mapping is relegated to the tail.

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 only a destructiveHint annotation and no output schema, the description covers the essential non-obvious behavior (deferred cancellation, retained access). It leaves out reversibility and auth expectations, so it is complete but not exhaustive.

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 all three parameters (including the two cancellation-reason fields) are already documented in the schema. The description adds no parameter-level meaning, so the baseline of 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 (cancel) and resource (subscription) plus the timing scope ('at the end of its current period'). It is clearly distinguishable from the get/list subscription siblings, though it never names an alternative to contrast against.

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?

Usage is implied by the purpose (call this when you want to cancel), and the end-of-period detail clarifies intent, but there is no explicit when-to-use/when-not guidance or comparison to sibling tools such as polar_get_subscription or polar_list_subscriptions.

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