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

With only destructiveHint=true from annotations, the description carries the burden well: it discloses the end-of-billing-period grace period, the resulting `cancelled` state, the real-customer impact, and the underlying API call. This is materially more than the annotation provides.

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 short sentences, front-loaded with the write/nature signal, then the lifecycle behavior, then the API reference. No filler or redundancy.

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 mutation with no output schema, the description covers purpose, lifecycle outcome, and real-world impact. Nothing an agent needs to call it correctly is missing.

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?

One required parameter with 100% schema description coverage, so the schema already documents `subscription_id`. The description adds no format or sourcing details for the id, so the 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?

States a specific verb and resource ('Cancel a subscription') and adds scope ('LIVE') plus a 'WRITE:' marker that separates it from the read-oriented get/list siblings. An agent can distinguish it from update_subscription without opening either schema.

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?

Usage is implied by the destructive nature and the 'LIVE subscription' qualifier, but the description never states when to prefer cancellation over siblings like update_subscription, nor any preconditions or exclusions. Adequate context but no explicit routing guidance.

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