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

Annotations already indicate non-read-only, non-destructive, and idempotent behavior. The description adds crucial behavioral details beyond annotations: ownership enforcement, deactivation rather than deletion, and that historical events remain accessible via recent_alerts. This enhances understanding of the operation's effects and constraints.

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?

Two sentences, with the core action front-loaded ('Cancel a subscription by id'). Each subsequent sentence adds distinct value: ownership enforcement and deactivation semantics. No redundancy or filler.

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 single-parameter tool with no output schema, the description sufficiently covers the operation, ownership requirement, and post-cancellation data availability. It does not explicitly describe the return value or error handling, but given the simplicity and annotations covering idempotency, this is a minor gap.

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?

The schema already describes the 'id' parameter as a subscription uuid. The description adds the important semantic that the id must belong to the caller ('you can only cancel your own subscriptions'), which is a constraint not present in the schema. This augments the parameter meaning beyond the basic type description.

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 description clearly states the function: 'Cancel a subscription by id.' It distinguishes itself from siblings like subscribe and list_subscriptions by specifying the action and resource. The additional details about ownership and deactivation further clarify its unique behavior.

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 provides clear context on when to use the tool: to cancel a subscription the user owns. It also gives a relevant alternative/consequence by noting that historical events remain available via recent_alerts, which helps the agent decide between cancellation and other actions. It does not explicitly name an alternative tool but the guidance is sufficient.

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