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

With no annotations provided, the description carries the full behavioral burden and does so well. It discloses billing semantics (pay-per-successful request, no monthly fee), clarifies that only 2xx responses are charged, and notes that API calls are blocked without a valid card.

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 front-loaded with the core action and then provides essential trigger conditions and billing context. It is slightly longer than strictly necessary, but every sentence adds relevant decision-making or behavioral information.

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 zero-parameter tool with no output schema, this description is complete. It covers when to call it, what the user must do with the result, how billing works, and the blocking condition, tying it together with sibling tools like register and get_api_info.

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 tool has zero parameters and 100% schema coverage by definition, so there is no parameter ambiguity. The baseline of 4 applies because no parameter documentation 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 uses a specific verb and resource: it retrieves a Stripe Checkout URL for adding or updating a credit card. This clearly distinguishes it from siblings like call_api, register, and get_api_info.

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: REQUIRED after registration and whenever a 402 error occurs. It also explains that the user must open the URL in a browser and that API calls are blocked until a card is on file, giving clear usage context.

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