Start checkout to add credit to the prepaid API balance and return a Stripe Checkout URL. Does NOT charge anything: the person must open the link. Transcription is billed at $0.20 per hour of audio. Requires an OAuth 2.1 user access token.
| Name | Required | Description | Default |
|---|---|---|---|
| amount_cents | Yes | Amount to add, in US cents. A project minimum applies. |
Changes observed during successful MCP inspections.
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Goes beyond annotations by explicitly stating that this operation does NOT charge anything and that the user must open the returned link to complete payment. It also discloses the OAuth 2.1 user token requirement and notes the per-hour billing context, giving the agent important behavioral and auth information.
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?
Three sentences, front-loaded with the core action and output, followed by essential clarifications. The pricing detail is slightly tangential but still useful context; overall there is no wasted wording.
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 simple one-parameter tool, the description covers the action, the returned value, the fact that no charge occurs until the link is opened, and the auth requirement. No critical information is missing for an agent to invoke 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 the sole parameter amount_cents is already documented as 'Amount to add, in US cents. A project minimum applies.' The description reinforces the purpose but does not add substantial new parameter-level detail beyond 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?
States a specific action ('Start checkout to add credit') and the output ('return a Stripe Checkout URL'). The resource (prepaid API balance) is named, and the tool is clearly differentiated from siblings like check_balance and get_billing_portal_url.
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 clearly conveys when to use the tool: when adding credit to the prepaid balance and initiating a Stripe checkout. It also clarifies the expected flow ('the person must open the link'), though it does not explicitly name alternatives or state when not to use it.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
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