x402-protected addition API on Base Sepolia accepting USDC micropayments
What it does
This endpoint is an x402-enabled API hosted on Vercel that appears to perform an addition operation (based on the `/api/add` path). It is part of an x402 AI starter project that demonstrates paid tool usage alongside unpaid tools. The endpoint requires an X-PAYMENT header with a valid x402 payment proof before returning results.
The endpoint accepts POST requests and is settled on the Base Sepolia testnet using USDC (contract 0x036CbD53842c5426634e7929541eC2318f3dCF7e). The maximum amount required per call is 5,000 base units of USDC, which equals $0.005 (half a cent) given USDC's 6 decimal places. Payments are sent to address 0x1e1A4566c750E1392Aa4fdb09C21f78E07f7E9AC with a timeout of 300 seconds. The x402 challenge version is 1 and uses the "exact" payment scheme.
Documentation is extremely sparse — no OpenAPI spec, no docs page, no README is available. The landing page suggests this is a demo/starter app showcasing paid vs. unpaid tool patterns for AI agents. The request body schema and response format are not documented, so the exact parameters for the addition operation must be inferred or discovered experimentally. Because this runs on a testnet (Base Sepolia), it is likely intended for development and testing rather than production use.
Capabilities
Use cases
- —Testing x402 payment flows with a simple arithmetic endpoint
- —Demonstrating paid tool integration for AI agents
- —Prototyping micropayment-gated API access on Base Sepolia
Fit
Best for
- —Developers learning x402 protocol integration
- —AI agent builders experimenting with paid tool calls
- —Testing x402 payment middleware on a testnet
Not for
- —Production arithmetic or computation needs
- —Mainnet payment workflows (this is testnet only)
- —Users needing documented, stable API contracts
Quick start
curl -X POST https://x402-ai-starter-flax.vercel.app/api/add \
-H "Content-Type: application/json" \
-H "X-PAYMENT: <x402_payment_proof>" \
-d '{"a": 2, "b": 3}'Example
Request
{
"a": 2,
"b": 3
}Endpoint
Quality
The endpoint is live and returns a valid x402 402 challenge, but there is no documentation, no OpenAPI spec, no examples, and no description of request/response schemas. The request body format is entirely inferred from the endpoint path name. This is a testnet demo/starter project with minimal information available.
Warnings
- —No documentation or OpenAPI spec available — request/response schema is unknown
- —Runs on Base Sepolia testnet; not suitable for production use
- —Request body format (e.g. {"a": N, "b": N}) is speculative based on the /api/add path
- —The example_request_json is inferred, not sourced from any documentation
Citations
- —Endpoint returns a valid x402 challenge with status 402 on POSThttps://x402-ai-starter-flax.vercel.app/api/add
- —Payment is settled on base-sepolia using USDC at contract 0x036CbD53842c5426634e7929541eC2318f3dCF7e with maxAmountRequired of 5000 base unitshttps://x402-ai-starter-flax.vercel.app/api/add
- —Landing page references paid tool, unpaid remote tool, and unpaid local tool patternshttps://x402-ai-starter-flax.vercel.app