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

Beyond the annotations (which already indicate mutation and non-destructive), the description adds critical behavioral context: ownership enforcement and the deactivation-vs-deletion distinction, pointing to recent_alerts for historical data.

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, front-loaded with the core action in the first sentence. Each sentence adds value: the first says what it does, the second explains the behavioral nuance.

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 description explains the ownership constraint, the non-destructive behavior, and where historical data remains. For a simple cancellation tool with annotations, this is sufficiently complete. It does not describe the return value, but that's not essential here.

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 fully documents the single 'id' parameter with a meaningful description (returned by subscribe). The tool description adds little parameter semantics, but given 100% schema coverage, this is acceptable per baseline.

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 uses a specific verb ('Cancel') and a clear resource ('a subscription by id'), distinguishing it from 'subscribe' and 'list_subscriptions' siblings. It also clarifies the outcome (deactivated, not deleted), which eliminates ambiguity.

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 context is clear: it's the tool to cancel a subscription you own. It doesn't explicitly mention alternatives, but the ownership constraint and the note about historical events provide sufficient guidance. Lacks explicit 'use when' but is evident from the title and description.

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