x402-protected addition endpoint on Base Sepolia accepting USDC testnet payments
What it does
This is a demo/starter x402 endpoint hosted on Vercel that gates access to a simple addition API behind a micropayment wall. The endpoint accepts POST requests at `/api/add` and requires an X-PAYMENT header conforming to the x402 protocol (version 1). Payment is settled on the Base Sepolia testnet using USDC (contract 0x036CbD53842c5426634e7929541eC2318f3dCF7e) with a maximum required amount of 5000 base units, which equals $0.005 (half a cent) given USDC's 6 decimals.
The landing page at the origin suggests this is part of an AI-agent starter kit that integrates paid and unpaid tools with models like GPT-4o and Gemini 2.0 Flash Lite. The endpoint is live and returns a proper 402 challenge with the `exact` payment scheme. However, there is no documentation, no OpenAPI spec, no usage examples, and no details about the request body schema or response format beyond the stated mimeType of `application/json`. The input schema only confirms it is an HTTP POST endpoint marked as discoverable.
Because this runs on Base Sepolia (a testnet), it is likely intended as a demonstration or development reference rather than a production service. Developers building x402-compatible agents can use it to test payment flows without spending real funds.
Capabilities
Use cases
- —Testing x402 payment flow integration in agent frameworks
- —Demonstrating micropayment-gated API access on Base Sepolia
- —Prototyping pay-per-call tool usage with AI agents
Fit
Best for
- —Developers learning the x402 protocol
- —Agent builders testing payment headers on testnet
- —Hackathon or demo projects needing a live x402 endpoint
Not for
- —Production arithmetic or computation workloads
- —Real-money transactions (this uses testnet USDC)
- —Users needing documented request/response schemas
Quick start
curl -X POST https://x402-ai-starter.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 402 challenge, but there is zero documentation, no OpenAPI spec, no response examples, and it operates on a testnet. The request body schema is entirely inferred from the endpoint name ('add'). This is effectively a stub/demo listing.
Warnings
- —No documentation available — /docs, /api, /pricing, /README all return 404
- —Request and response schemas are completely unknown; the example request is inferred from the endpoint name
- —Runs on Base Sepolia testnet — USDC here has no real monetary value
- —No OpenAPI or ai-plugin manifest found
- —This appears to be a starter/demo project, not a production service
Citations
- —Endpoint returns a valid x402 version 1 challenge with status 402https://x402-ai-starter.vercel.app/api/add
- —Payment is in USDC on Base Sepolia with maxAmountRequired of 5000 base units ($0.005)https://x402-ai-starter.vercel.app/api/add
- —USDC asset contract is 0x036CbD53842c5426634e7929541eC2318f3dCF7ehttps://x402-ai-starter.vercel.app/api/add
- —Landing page references GPT-4o, Gemini 2.0 Flash Lite, and paid/unpaid toolshttps://x402-ai-starter.vercel.app