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

Annotations already declare readOnlyHint=true, destructiveHint=false, and idempotentHint=true, so the safety profile is clear. The description adds valuable behavioral context by specifying it returns the caller's own subscriptions only ('caller's active') and enumerates the response fields, which is beyond what annotations provide.

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, front-loaded with the core action, and every sentence earns its place. The first sentence states purpose and return fields; the second gives usage context. No wasted words, perfectly sized.

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 one optional parameter, the description provides complete context: what it lists, what fields are returned, and when to use it. The schema covers the parameter, annotations cover safety, and the description covers the return format and usage scenarios. 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 schema provides 100% coverage with a clear description for the include_inactive parameter. The tool description does not explicitly mention this parameter, but it implicitly references active subscriptions. Since the schema fully documents the parameter, the baseline of 3 is appropriate; the description adds no extra parameter semantics.

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 the specific verb 'List' and clearly identifies the resource as 'the caller's active subscriptions.' It also lists the exact fields returned, making the tool's purpose unambiguous and distinguishing it from sibling tools like subscribe and unsubscribe.

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 provides explicit guidance on when to use the tool: 'Use this to review what you're monitoring before adding more or to find an id to cancel.' This directly connects to related actions (subscribe/unsubscribe) and gives clear use cases, effectively guiding the agent.

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