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

Annotations only show readOnlyHint=false, but the description goes beyond by explaining the side effect (proration, settings URL returned instead), the payment webhook dependency, and the requirement to call get_account afterward. This adds important behavioral context not present in annotations, such as the fact that access is granted asynchronously.

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 concise yet dense, front-loading the core purpose (checkout URL) and immediately providing essential pricing details. Every sentence adds value—no fluff, and it efficiently covers usage, safety, and post-call actions in a compact form.

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?

The description is complete for a tool with only two optional parameters and no output schema. It covers the return value, the alternate behavior, the dependency on a webhook, and the follow-up action, leaving nothing an agent needs to know to call it 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?

Schema coverage is 100% and enums define valid values, so the schema already documents the parameters. The description adds the pricing tiers and the yearly discount, which enriches the meaning, but the baseline is 3 because the schema already does the heavy lifting; no additional syntax or format details are 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 clearly states it returns a Stripe Checkout URL for a plan, with explicit pricing and interval details. It distinguishes itself from other tools by focusing on the checkout link generation, while also noting the alternate behavior for active subscriptions, which differentiates it from a simple billing 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?

It explicitly tells the agent when to use it (when a user needs to pay or switch plans), and when not to (never enter payment details, and call get_account after webhook confirms access). It also implies the alternative path for existing subscriptions, providing clear decision guidance.

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