x402-protected addition endpoint on Base Sepolia accepting USDC micropayments
What it does
This is a simple x402-enabled API endpoint hosted on Vercel that performs an addition operation behind a paywall. It accepts POST requests and requires an x402 payment header to access. The endpoint is part of an AI starter template that demonstrates how to integrate x402 payment gating with AI tool usage.
The endpoint charges up to 0.005 USDC (5000 base units with 6 decimals) per request on the Base Sepolia testnet. Payments are settled in USDC to the specified wallet address. The x402 challenge advertises version 1 of the protocol using the "exact" payment scheme, with a maximum timeout of 300 seconds for payment settlement.
The landing page suggests this is a demo application that integrates paid and unpaid tools with LLM models (GPT-4o, Gemini 2.0 Flash Lite). No formal documentation, OpenAPI schema, or detailed API reference is available. The endpoint's input/output schema beyond the basic HTTP POST method and JSON mime type is not documented, so the exact request body format for the addition operation must be inferred or discovered experimentally.
Capabilities
Use cases
- —Testing x402 payment protocol integration with a simple arithmetic endpoint
- —Demonstrating how AI agents can use paid tools via x402 headers
- —Prototyping micropayment-gated API workflows on Base Sepolia testnet
Fit
Best for
- —Developers learning the x402 payment protocol
- —AI agent builders experimenting with paid tool calls
- —Testnet-based micropayment proof-of-concept work
Not for
- —Production arithmetic or computation workloads
- —Mainnet payment use cases (this runs on Base Sepolia testnet)
- —Users needing documented, stable API contracts
Quick start
curl -X POST https://x402-ai-starter-alpha.vercel.app/api/add \
-H "Content-Type: application/json" \
-H "X-PAYMENT: <x402_payment_token>" \
-d '{"a": 2, "b": 3}'Example
Request
{
"a": 2,
"b": 3
}Endpoint
Quality
The endpoint is live and returns a valid x402 challenge, but there is no documentation, no OpenAPI schema, no examples, and no description of the request/response format. The request body shape (e.g., {"a", "b"}) is entirely inferred from the endpoint name '/api/add'. This is effectively a testnet demo stub with minimal discoverable information.
Warnings
- —No documentation available — /docs, /api, /pricing, /README all return 404
- —Request and response body schemas are not documented; the example request is inferred from the endpoint name only
- —Runs on Base Sepolia testnet — not suitable for production or real-value transactions
- —This appears to be a starter/demo application, not a production service
Citations
- —Endpoint returns x402 version 1 challenge with exact scheme on base-sepolia network, max amount 5000 base units in USDChttps://x402-ai-starter-alpha.vercel.app/api/add
- —USDC asset address is 0x036CbD53842c5426634e7929541eC2318f3dCF7e on Base Sepoliahttps://x402-ai-starter-alpha.vercel.app/api/add
- —Landing page references paid tool usage with GPT-4o and Gemini 2.0 Flash Litehttps://x402-ai-starter-alpha.vercel.app