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

While annotations indicate non-read-only and external world interaction, the description goes far beyond by explaining that it creates an external checkout session, does not charge the card, cannot complete payment, and that credit is applied only after human payment completion. It also notes the tool is not metered. This provides valuable behavioral context the annotations do not cover, with no contradictions.

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 consists of four sentences, each conveying essential information: purpose, side-effect behavior, user action required, and usage trigger. It is front-loaded with the main purpose and avoids unnecessary wording. While not as terse as a single sentence, the extra length is justified by the need to explain external payment flow clearly.

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 tool with one parameter and an existing output schema, the description is complete. It covers purpose, usage conditions, behavioral caveats, and the critical requirement to return the URL to a human. The presence of an output schema means the return value need not be explained. No significant gaps remain for an agent to correctly invoke this tool.

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 description provides full coverage for the single parameter (amountUsd) with min, max, and common block examples. The tool description itself adds no additional parameter semantics, so it does not exceed the baseline of 3 when schema coverage is high. The description does not redundantly repeat schema information, which is acceptable.

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 creates a Stripe Checkout URL for adding prepaid credit to the calling Bearer API key. It distinguishes itself from sibling tools (which are about API discovery, auth, and key management) by specifying the exact resource and action. The verb 'create' and specific resource 'Stripe Checkout URL' make the purpose highly unambiguous.

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 instructs when to use the tool: after an HTTP 402 or when balance is low. It also clarifies that the tool itself is not metered, which prevents misuse. It and states that the agent cannot complete payment, so the URL must be returned to a human, providing clear usage context. No alternatives exist among siblings, so no exclusions are needed.

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