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

Beyond the annotations (which already indicate mutation, idempotency, and non-destructiveness), the description adds meaningful behavioral context: ownership enforcement and the deactivation-not-deletion mechanism. It explicitly explains that the row is deactivated to preserve historical events, which directly complements the destructiveHint=false annotation. This is valuable non-redundant disclosure.

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 clear sentences: the first states the core action, the second covers ownership and side effects. Every sentence earns its place with zero wasted words, and the key verb 'Cancel' is front-loaded.

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?

The tool is simple (one parameter, no output schema, no nested objects), and the description fully covers its purpose, ownership rules, and behavioral consequence (deactivation). It also links to recent_alerts for historical events, making the tool's place in the larger workflow clear. The description is complete for this level of complexity.

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 input schema already covers 100% of parameter descriptions, with 'id' documented as 'Subscription id (uuid) returned by subscribe.' The description adds only the ownership nuance ('you can only cancel your own subscriptions'), which is a behavioral note rather than parameter syntax or format details. This does not significantly exceed schema coverage, so the baseline of 3 is appropriate.

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 opens with 'Cancel a subscription by id,' which uses a specific verb ('Cancel') and resource ('subscription'), and clearly distinguishes this from siblings like subscribe (create) and list_subscriptions (list). The ownership constraint further clarifies the exact scope.

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 states ownership is enforced and explains the deactivation behavior ('deactivated not deleted'), giving clear context for when to use this tool vs alternatives. It implies use for canceling your own subscriptions and notes historical events remain via recent_alerts, but it does not explicitly name sibling alternatives or when not to use it, so it falls just short of a 5.

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