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

Adds value beyond annotations: describes deactivation vs deletion, ownership enforcement, and availability of historical events. Annotations indicate mutation but not destructive; description confirms. No contradiction.

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 concise sentences, front-loaded with action, then constraints, then side effects. No redundant information.

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?

Adequate for a simple mutation with one parameter. Covers behavior, ownership, and effect on history. Could mention return value, but details are sufficient for agent invocation.

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 covers 100% of parameter details. Description adds minimal extra meaning (ownership context), but baseline 3 is appropriate since schema already explains the parameter.

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?

Clear verb ('cancel') and resource ('subscription'), with specific scope ('by id'). Distinguishes from siblings like subscribe and list_subscriptions by stating ownership and deactivation behavior.

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'), which defines when to use. Does not list alternatives but context from siblings is clear.

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