PayWatcherHow AI Agents Pay for API Calls — And How to Verify They Did
The x402 protocol just made machine-to-machine payments real. Here's what the verification layer looks like.
PayWatcherHow to Verify USDC Payments on Base Without a Payment Processor
Accept stablecoin payments with 3 lines of code. No custody, no checkout flow, no percentage fees. Just verification.
PayWatcherHow to Accept AI Agent Payments with x402 + PayWatcher
PayWatcher · April 2026
Payment verification without the payment processor. Works like Stripe Payment Intents, but for on-chain USDC. Non-custodial. Flat-rate. Three API calls.
PayWatcherHow AI Agents Pay for API Calls — And How to Verify They Did
The x402 protocol just made machine-to-machine payments real. Here's what the verification layer looks like.
PayWatcherHow to Verify USDC Payments on Base Without a Payment Processor
Accept stablecoin payments with 3 lines of code. No custody, no checkout flow, no percentage fees. Just verification.
PayWatcherHow to Accept AI Agent Payments with x402 + PayWatcher
PayWatcher · April 2026
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Payment verification without the payment processor. Works like Stripe Payment Intents, but for on-chain USDC. Non-custodial. Flat-rate. Three API calls.
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We've been quietly shipping for the past few months. Here's what PayWatcher is and why we built it on Base.
The problem
Every developer building with stablecoins runs into the same wall: you need to know when a USDC payment has arrived on-chain. Polling the blockchain yourself is brittle. Existing payment processors take a percentage cut or hold your funds in custody. Neither makes sense for stablecoin-native applications.
What we built
PayWatcher is a USDC payment verification API. Non-custodial, developer-first, $0.05 flat fee per verification.
You tell PayWatcher which payment you expect — the amount, the deposit address, the chain. It watches the blockchain and fires a signed webhook the moment the payment is confirmed. That's it.
No percentage. No custody. No lock-in. Just: did the payment arrive?
What's live today
Multi-chain EVM backend: Base, Arbitrum, Ethereum, Optimism, Polygon
POST /v1/payments/verify — x402 native, no API key required
GET /v1/verifications — for dashboards and agent workflows
Frontend: landing page, dashboard, interactive demo at paywatcher.dev/demo
CI/CD integration tests across 5 testnets
Why x402
PayWatcher is one of the few projects running x402 verification in production. AI agents can verify USDC payments on Base without an API key — just HTTP 402 + txHash. We built the verification layer that makes x402-based payment flows reliable.
What's next
A PayWatcher MCP Server at api.paywatcher.dev/mcp — agents call PayWatcher tools directly and pay per call via x402. No account, no onboarding. Connect, pay, verify.
ChainSights (our governance data API) will use PayWatcher internally as its x402 verification layer — dogfooding the stack end-to-end.
The ask
We're applying for a Base Builder Grant (1-3 ETH) to cover infrastructure costs — Vercel Pro, Alchemy RPC, tooling — and accelerate the MCP server launch.
If you're building with x402 or stablecoin payments on Base, we'd love to connect.
→ paywatcher.dev → @paywatcher on Farcaster, @X_Sem_pre on X
Mario Semper — masemIT e.U., Austria. Solo founder, building in public.
We've been quietly shipping for the past few months. Here's what PayWatcher is and why we built it on Base.
The problem
Every developer building with stablecoins runs into the same wall: you need to know when a USDC payment has arrived on-chain. Polling the blockchain yourself is brittle. Existing payment processors take a percentage cut or hold your funds in custody. Neither makes sense for stablecoin-native applications.
What we built
PayWatcher is a USDC payment verification API. Non-custodial, developer-first, $0.05 flat fee per verification.
You tell PayWatcher which payment you expect — the amount, the deposit address, the chain. It watches the blockchain and fires a signed webhook the moment the payment is confirmed. That's it.
No percentage. No custody. No lock-in. Just: did the payment arrive?
What's live today
Multi-chain EVM backend: Base, Arbitrum, Ethereum, Optimism, Polygon
POST /v1/payments/verify — x402 native, no API key required
GET /v1/verifications — for dashboards and agent workflows
Frontend: landing page, dashboard, interactive demo at paywatcher.dev/demo
CI/CD integration tests across 5 testnets
Why x402
PayWatcher is one of the few projects running x402 verification in production. AI agents can verify USDC payments on Base without an API key — just HTTP 402 + txHash. We built the verification layer that makes x402-based payment flows reliable.
What's next
A PayWatcher MCP Server at api.paywatcher.dev/mcp — agents call PayWatcher tools directly and pay per call via x402. No account, no onboarding. Connect, pay, verify.
ChainSights (our governance data API) will use PayWatcher internally as its x402 verification layer — dogfooding the stack end-to-end.
The ask
We're applying for a Base Builder Grant (1-3 ETH) to cover infrastructure costs — Vercel Pro, Alchemy RPC, tooling — and accelerate the MCP server launch.
If you're building with x402 or stablecoin payments on Base, we'd love to connect.
→ paywatcher.dev → @paywatcher on Farcaster, @X_Sem_pre on X
Mario Semper — masemIT e.U., Austria. Solo founder, building in public.
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