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

The description reveals key behavioral traits beyond annotations: ownership enforcement and that rows are deactivated (not deleted). Annotations indicate non-destructive mutation; the description adds nuance that historical events remain available. No contradiction with annotations.

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?

The description is two sentences long, front-loads the core purpose, and includes essential usage details without any fluff. Every sentence adds value.

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?

Given the tool's simplicity (single parameter, no output schema, clear annotations), the description covers all necessary aspects: purpose, usage constraints, and side effects. No gaps.

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 includes a thorough description for the single required parameter ('Subscription id (uuid) returned by subscribe.'), achieving 100% coverage. The tool description adds no additional context about the parameter beyond what the schema provides.

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?

Description clearly states 'Cancel a subscription by id.' It uses a specific verb (cancel/unsubscribe) and identifies the resource (subscription). The sibling tools include 'subscribe' and 'list_subscriptions', making this tool's purpose distinct.

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 explicitly mentions ownership enforcement: 'you can only cancel your own subscriptions.' This provides clear context on when the tool can be used. It also explains that the row is deactivated, not deleted, which indirectly advises against using it if one expects deletion. However, it does not explicitly discuss alternative tools or when not to use it.

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