x402 Agent Wallet Tools: X402 Duplicate Charge Guard

Overview

Detect duplicate x402 transactions, repeated order deliveries, and replay-prone payment records before settlement or entitlement release. Wallet signing safety pack first: $0.018 for buyer-owned controls and enforcement policy, with a free receipt-gate preview plus duplicate-charge, EIP-712, allowance, Permit2, simulation, and spend guards. Start buyer evaluation at https://x402-wallet.558686.xyz/x402/buyer-use-cases or machine JSON https://x402-wallet.558686.xyz/x402/buyer-use-cases.json; checkout contract JSON is https://x402-wallet.558686.xyz/x402/checkout.json. Route payment activation JSON is https://x402-wallet.558686.xyz/x402/route/x402-duplicate-charge-guard/payment-activation.json. Browsers can inspect the quote, but payment requires a buyer-owned runtime that signs and retries the same request with X-PAYMENT. Buyers can download the route-specific first-payment client at https://x402-wallet.558686.xyz/x402/route/x402-duplicate-charge-guard/first-payment-client.mjs, run node first-payment-client.mjs for quote-only checks, then opt into a buyer-owned x402 payment with PAY_REAL_X402=1. Copy-ready first paid request: curl -fsSL https://x402-wallet.558686.xyz/x402/route/x402-duplicate-charge-guard/first-payment-client.mjs -o first-payment-client.mjs && npm install @x402/fetch @x402/core @x402/evm viem && PAY_REAL_X402=1 EVM_PRIVATE_KEY=$EVM_PRIVATE_KEY node first-payment-client.mjs. Generic clients can also discover it from the live 402 response headers: the standard Payment-Required header includes firstPaymentClient, paymentClientUrl, and sameRequestRetryRequired pointers; X-First-Payment-Client, X-Download-Install-Then-Pay-Command, and Link rel=payment-client mirror the same handoff.

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