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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so the safety profile is covered. The description adds valuable context by specifying the scope ('caller's') and the exact return fields (id, type, params, etc.), which is not present in the schema or annotations. 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?

Exactly two sentences: the first states the action and return fields, the second states the intended use cases. No filler, every word earns its place.

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 simple list tool with no output schema, the description includes the return fields and explicit usage guidance. Annotations handle safety semantics. This is complete for its complexity level.

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 has 100% coverage for its single parameter, include_inactive, with a clear description. The tool description does not add any additional meaning about this parameter, so the baseline of 3 is appropriate given that the schema does the heavy lifting.

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 opens with 'List the caller's active subscriptions,' a specific verb+resource statement that clearly distinguishes this from sibling tools like subscribe and unsubscribe. It also enumerates the fields returned, further clarifying the tool's exact purpose.

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 second sentence explicitly tells the caller when to use this: 'before adding more' subscriptions or 'to find an id to cancel.' This gives clear usage context, though it doesn't explicitly name alternative tools or state when not to use it, which is why it doesn't reach a 5.

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