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

The description discloses key behavioral traits: it creates an external checkout session but does not charge a card, and credit is applied only after the human completes payment. It also notes that the tool is not metered. While annotations indicate readOnlyHint=false (so it's not read-only), the description adds important context about the external session and the need for human action, which goes beyond the annotations.

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 and well-structured. It front-loads the core purpose, then explains the limitation (cannot complete payment), and finally provides usage context. Every sentence adds value, and the description is appropriately sized for the tool's complexity.

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?

Given the tool's simplicity (one parameter, no nested objects) and the presence of an output schema, the description is complete. It covers the purpose, usage context, behavioral limitations, and the need for human involvement. The output schema likely describes the returned URL, so the description doesn't need to explain return values. This is a well-rounded description.

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 a description for the single parameter 'amountUsd' with common blocks (10, 50, 200). The description adds context by explaining that the amount is for prepaid credit, but it doesn't add much beyond the schema. Since schema coverage is 100% and the parameter is well-documented, a score of 4 is appropriate, as the description reinforces the purpose but doesn't introduce new semantics.

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 the tool's purpose: 'Create a Stripe Checkout URL for adding prepaid credit to the calling Bearer API key.' It specifies the verb (create), the resource (top-up link), and the mechanism (Stripe Checkout URL). It also distinguishes itself from siblings by focusing on the top-up link creation, which is unique among the listed tools.

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 provides explicit usage guidance: 'Use after HTTP 402 or when balance is low; the tool itself is not metered.' It also clarifies that the tool cannot complete the payment and the URL must be returned to a human, which is a clear when-to-use and when-not-to-use instruction. This is excellent guidance for an agent.

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