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

Annotations already show readOnlyHint=false, openWorldHint=true, and destructiveHint=false, so the description appropriately adds side-effect context: nothing is charged until the user completes payment on Stripe. It also explains what the billing page contains and the refund policy, which goes beyond the boolean hints.

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 purpose is front-loaded in the first sentence, and the rest covers pricing, features, and refund policy in a dense block. It is slightly longer than strictly necessary for tool invocation, but every sentence carries relevant business context and there is no fluff.

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 single-optional-parameter tool with no output schema, the description is complete: it identifies the output as a link, explains both billing states, covers pricing and payment timing, and notes the refund guarantee. Nothing essential for selecting or invoking the tool is missing.

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 already provides 100% coverage for the only parameter, 'billed', including the monthly/yearly values and the fact that it is ignored for existing subscribers. The description repeats pricing details that are also in the schema, but it does not add meaningfully new parameter-level semantics beyond the schema.

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 a specific action ('Get a link') and precisely defines the two outcomes: a subscription link for new buyers and a billing-management page for existing subscribers. It unambiguously distinguishes this tool from any billing-related sibling and leaves no doubt about what invoking it returns.

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 separates the two use cases: new subscribers get a Pro subscription link, while already-paying accounts get the billing page with card, invoices, and cancellation. It also tells the agent to hand the link to the person and notes that no charge occurs until the Stripe flow is finished.

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