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

Annotations already flag this as a non-idempotent write with open-world effects, and the description adds meaningful detail beyond them: an external Stripe payment step, the guarantee that "Credits are added automatically after payment," and exactly what the call returns. It stops short of saying whether repeat calls create multiple independent checkout links, which matters given idempotentHint=false.

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?

Four short sentences, front-loaded with the action, then pricing, then what to do with the result, then the post-payment effect. Nothing is redundant or padded.

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 two-parameter tool with no output schema, the description covers what is produced (checkout_url), how to deliver it, and what happens after payment, which is what an agent needs to complete the workflow. The one omission is disambiguation from the USDC sibling.

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%, so the baseline is 3, but the description adds genuine meaning by mapping each enum value to concrete value: starter = 1000 credits/$3, pro = 5000/$10, business = 15000/$20. That lets an agent choose a plan without extra lookups; only the api_key parameter is left to 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 verb and resource: "Create a Stripe checkout link to top up this API key." The mention of Stripe implicitly separates it from the sibling buy_credits_usdc, so an agent can tell which credit-purchase tool applies.

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 explains what to do with the result ("Give the returned checkout_url to your user to pay (or complete it if you can make payments)"), which is real usage guidance for the post-call step. However, it never states when to prefer this over buy_credits_usdc or get_pricing, and gives no prerequisites beyond the optional API key.

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