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

Annotations already declare readOnlyHint and idempotentHint, and the description adds meaningful behavioral detail: it cannot spend money or start/change/cancel subscriptions. It also adds the key domain rule that plans gate depth, never truth, so the agent will not present upgrades as changing registration verdicts.

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 rich but somewhat verbose, with repeated emphatic phrasing such as 'Paying buys more of the picture, never a different answer about reality.' It makes its key points, but multiple sentences restate the same idea, and the all-caps phrase adds weight more than clarity.

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?

There is no output schema, so the description carries the burden of explaining the return value. It specifies that available plans, inclusions, current tier, allowances used, and invariant truths are listed. Combined with the zero parameters and safety annotations, this is complete enough for an agent to invoke the tool correctly.

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, and schema coverage is 100%, so there is nothing for the description to add about parameters. The baseline of 4 applies because no parameter guidance is needed.

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 states a clear verb and resource: 'Show the available plans with what each includes, plus the caller's current tier and any allowance they have used.' It also clarifies the purpose by tying it to real user needs like asking for tier costs or hitting limits. This clearly differentiates it from reading as a generic pricing or subscription tool.

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 explicitly states when to use the tool: when the user asks about tier costs, bumps into a limit, or when a refusal points to an exhausted allowance. It does not name alternative tools or explicitly say when not to use it, leaving some sibling differentiation to inference.

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