{"id":"a205b9f6-e779-4049-8bfa-9bfdc0a39add","shortId":"BUFyJ2","kind":"x402","title":"x402-protected addition endpoint on Base Sepolia accepting USDC testnet payments","tagline":"x402-protected addition endpoint on Base Sepolia accepting USDC testnet payments","description":"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.\n\nThe 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.\n\nBecause 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.","tags":[],"capabilities":["x402-payment-gating","http-post","json-response","base-sepolia-testnet","usdc-micropayment","exact-payment-scheme"],"categories":["demo","x402","math"],"synonyms":["x402 starter","paid API demo","micropayment addition","base sepolia x402","x402 vercel example","paid tool demo"],"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"],"endpointUrl":"https://x402-ai-starter.vercel.app/api/add","protocol":"x402","transport":"http","auth":{"type":"x402","details":[{"asset":"0x036CbD53842c5426634e7929541eC2318f3dCF7e","extra":{"name":"USDC","version":"2"},"payTo":"0x78397B97E4CC96Ddb46FDeAE391b05546316A218","scheme":"exact","network":"base-sepolia","mimeType":"application/json","resource":"https://x402-ai-starter.vercel.app/api/add","description":"Access to protected content","outputSchema":{"input":{"type":"http","method":"POST","discoverable":true}},"maxAmountRequired":"5000","maxTimeoutSeconds":300}]},"qualityScore":"0.300","qualityRationale":"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 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'0.005':90 '0x036cbd53842c5426634e7929541ec2318f3dcf7e':78 '1':66 '2.0':130 '402':141 '4o':127 '5000':85 '6':97 'accept':9,21,48 'access':36 'addit':4,16,40 'agent':113,218 'ai':112 'ai-ag':111 'amount':83 'api':41 'application/json':175 'base':7,19,72,86,194 'base sepolia x402' 'base-sepolia-testnet' 'behind':42 'beyond':170 'bodi':165 'build':214 'cent':93 'challeng':142 'compat':217 'confirm':180 'conform':60 'contract':77 'decim':98 'demo/starter':28 'demonstr':204 'detail':161 'develop':206,213 'discover':189 'document':152 'endpoint':5,17,30,47,134,186 'equal':89 'exact':145 'exact-payment-scheme' 'exampl':158 'flash':131 'flow':225 'format':169 'fund':229 'gate':35 'gemini':129 'given':94 'gpt':126 'gpt-4o':125 'half':91 'header':59 'host':31 'howev':148 'http':184 'http-post' 'input':177 'integr':117 'intend':201 'json-response' 'kit':115 'land':100 'like':124,200 'lite':132 'live':136 'mark':187 'maximum':81 'micropay':44 'micropayment addition' 'mimetyp':173 'model':123 'openapi':154 'origin':104 'page':101 'paid':118 'paid API demo' 'paid tool demo' 'part':108 'payment':12,24,58,67,146,224 'post':49,185 'product':211 'proper':140 'protect':3,15 'protocol':64 'rather':208 'real':228 'refer':207 'request':50,164 'requir':54,82 'respons':168 'return':138 'run':192 'schema':166,178 'scheme':147 'sepolia':8,20,73,195 'servic':212 'settl':69 'simpl':39 'spec':155 'spend':227 'starter':114 'state':172 'suggest':105 'test':223 'testnet':11,23,74,197 'tool':121 'unit':87 'unpaid':120 'usag':157 'usdc':10,22,76,95 'usdc-micropayment' 'use':75,220 'vercel':33 'version':65 'wall':45 'without':226 'x':57 'x-payment':56 'x402':2,14,29,63,216 'x402 starter' 'x402 vercel example' 'x402-compatible':215 'x402-payment-gating' 'x402-protected':1,13","prices":[{"id":"80d02b0d-05c6-49c2-aa48-db9c9f8959d5","listingId":"a205b9f6-e779-4049-8bfa-9bfdc0a39add","amountUsd":null,"unit":"per_call","nativeCurrency":"USDC","nativeAmount":"5000","chain":"base-sepolia","payTo":"0x78397B97E4CC96Ddb46FDeAE391b05546316A218","paymentMethod":"x402-usdc","isPrimary":true,"details":{"scheme":"exact","mime_type":"application/json","accepts_all":[{"asset":"0x036CbD53842c5426634e7929541eC2318f3dCF7e","extra":{"name":"USDC","version":"2"},"payTo":"0x78397B97E4CC96Ddb46FDeAE391b05546316A218","scheme":"exact","network":"base-sepolia","mimeType":"application/json","resource":"https://x402-ai-starter.vercel.app/api/add","description":"Access to protected content","outputSchema":{"input":{"type":"http","method":"POST","discoverable":true}},"maxAmountRequired":"5000","maxTimeoutSeconds":300}],"asset_contract":"0x036CbD53842c5426634e7929541eC2318f3dCF7e","max_timeout_seconds":300},"createdAt":"2026-04-21T18:32:34.564Z"}],"sources":[{"listingId":"a205b9f6-e779-4049-8bfa-9bfdc0a39add","source":"x402_bazaar","sourceId":"https://x402-ai-starter.vercel.app/api/add","sourceUrl":"https://api.cdp.coinbase.com/platform/v2/x402/discovery/resources","isPrimary":true,"firstSeenAt":"2026-04-21T18:32:34.564Z","lastSeenAt":"2026-04-22T04:02:49.926Z"}],"details":{"listingId":"a205b9f6-e779-4049-8bfa-9bfdc0a39add","quickStartSnippet":"curl -X POST https://x402-ai-starter.vercel.app/api/add \\\n  -H \"Content-Type: application/json\" \\\n  -H \"X-PAYMENT: <x402-payment-token>\" \\\n  -d '{\"a\": 2, \"b\": 3}'","exampleRequest":{"a":2,"b":3},"exampleResponse":null,"schema":{"input":{"type":"http","method":"POST","discoverable":true}},"openapiUrl":null,"agentsTxtUrl":null,"citations":[{"claim":"Endpoint returns a valid x402 version 1 challenge with status 402","source_url":"https://x402-ai-starter.vercel.app/api/add"},{"claim":"Payment is in USDC on Base Sepolia with maxAmountRequired of 5000 base units ($0.005)","source_url":"https://x402-ai-starter.vercel.app/api/add"},{"claim":"USDC asset contract is 0x036CbD53842c5426634e7929541eC2318f3dCF7e","source_url":"https://x402-ai-starter.vercel.app/api/add"},{"claim":"Landing page references GPT-4o, Gemini 2.0 Flash Lite, and paid/unpaid tools","source_url":"https://x402-ai-starter.vercel.app"}],"useCases":["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"],"bestFor":["Developers learning the x402 protocol","Agent builders testing payment headers on testnet","Hackathon or demo projects needing a live x402 endpoint"],"notFor":["Production arithmetic or computation workloads","Real-money transactions (this uses testnet USDC)","Users needing documented request/response schemas"],"kindDetails":{"x402_version":1,"resource_type":"http","bazaar_last_updated":"2026-04-17T19:30:06.462Z"},"updatedAt":"2026-04-22T04:02:49.926Z"}}