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

Adds value beyond annotations: discloses deactivation instead of deletion, ownership enforcement, and impact on historical data. Annotations already indicate non-destructive and idempotent behavior; description complements with concrete details.

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 sentences with no redundancy. First sentence states action, second adds constraint, third explains effect. Front-loaded and efficient.

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 fully covers behavior, constraints, and side effects. Annotations handle idempotency and destructiveness; description adds ownership and lifecycle details.

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 already describes 'id' as 'Subscription id (uuid) returned by subscribe.' with 100% coverage. Description does not add new semantic meaning for the parameter, so baseline 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?

Clearly states 'Cancel a subscription by id' – specific verb and resource. Distinguishes from siblings like 'subscribe' and 'list_subscriptions' by focusing on cancellation and mentioning deactivation vs deletion.

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?

Explicitly states ownership enforcement ('you can only cancel your own subscriptions'), guiding when not to use. Also notes that historical events remain via recent_alerts, implying a context where this tool is preferred over deletion.

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