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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false. The description adds valuable behavioral detail beyond annotations: the exact return shape, optional trial fields, stable plan_type values, and the important semantic that a limit of 0 means unlimited for Premium plans. This fully explains what the tool returns and how to interpret it.

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 well-structured with a clear 'Returns:' section, uses recognizable type names, and explains edge-case semantics concisely. Every sentence adds value with no filler.

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?

Given this is a parameterless read-only operation with annotations covering safety and an output schema absent, the description is complete. It describes all returned fields, their types, optionality, and meaning, leaving no ambiguity for an agent invoking the tool.

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?

There are zero parameters, so the input schema has no burden. The description adds no parameter documentation because none is needed. Baseline 4 is appropriate for a parameterless tool.

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 names a specific verb and resource ('Get the user's subscription plan, limits, and trial status') and clearly distinguishes this read-only status tool from subscription lifecycle tools like cancel_subscription, reactivate_subscription, and list_subscription_plans. It tells an agent exactly what information is available.

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: use this when you need the current user's subscription plan, limits, or trial status. It does not explicitly list alternatives or say when not to use it, but the purpose is specific enough that an agent can infer the right situation.

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