{
  "format": "delx/intent-card/v1",
  "id": "x402-payment-nonce-check-api",
  "intent": "X402 Payment Nonce Check for an agent workflow",
  "title": "X402 Payment Nonce Check API for agents",
  "description": "X402 Payment Nonce Check: X402 Payment Nonce Check checks a payment nonce for presence, length, and caller-known reuse from bounded caller-supplied values without an external provider. Call X402 Payment Nonce Check before paying for or accepting an x402 or agent delivery assembled from caller-supplied challenge and result metadata. Returns contract-specific checks, normalized evidence, mismatch reasons, and an explicit acceptance or rejection status for X402 Payment Nonce Check as versioned deterministic JSON. Price: $0.001 USDC via x402 on Base. First-party, stateless, memory-only execution with no paid upstream, live RPC, web search, credentials, custody, signing, media generator, or input retention. Honest limit: Validates metadata only; it never settles payment, signs payloads, contacts a facilitator, refunds funds, or asserts on-chain truth. Advisory output only; the buyer owns authorization, payment policy, and production decisions.",
  "keywords": [
    "X402 Payment Nonce Check API",
    "X402 Payment Nonce Check for agents",
    "pay per result API",
    "x402 API",
    "no API key"
  ],
  "updated_at": "2026-08-23",
  "canonical_url": "https://commerce.delx.ai/intents/x402-payment-nonce-check-api",
  "machine_url": "https://commerce.delx.ai/intents/x402-payment-nonce-check-api.json",
  "recommendation": {
    "tool_name": "util_x402_payment_nonce_check",
    "service_name": "X402 Payment Nonce Check",
    "method": "POST",
    "resource": "https://api.delx.ai/api/v1/x402/x402-payment-nonce-check",
    "price_usdc": "0.001",
    "payment_protocols": [
      "x402",
      "mpp"
    ],
    "input_schema": {
      "$schema": "https://json-schema.org/draft/2020-12/schema",
      "type": "object",
      "properties": {
        "nonce": {
          "type": "string",
          "maxLength": 8192,
          "description": "Nonce supplied to X402 Payment Nonce Check; used only for this bounded calculation and processed in memory without retention."
        },
        "seen_nonces": {
          "type": "array",
          "maxItems": 256,
          "items": {
            "type": "string",
            "maxLength": 8192
          },
          "description": "Seen Nonces supplied to X402 Payment Nonce Check; used only for this bounded calculation and processed in memory without retention."
        },
        "minimum_length": {
          "type": "integer",
          "description": "Minimum Length supplied to X402 Payment Nonce Check; used only for this bounded calculation and processed in memory without retention."
        }
      },
      "required": [
        "nonce",
        "seen_nonces",
        "minimum_length"
      ],
      "additionalProperties": false
    },
    "example_input": {
      "nonce": "order-42-attempt-1",
      "seen_nonces": [
        "order-41-attempt-1"
      ],
      "minimum_length": 8
    },
    "example_output": {
      "schema": "delx/util-x402-payment-nonce-check/v1",
      "operation": "delivery_contract:x402_payment_nonce_check",
      "status": "pass",
      "result": {
        "nonce_length": 18,
        "reused": false,
        "accepted": true
      },
      "evidence": {
        "input_sha256": "5b10e7096699f6b6a1dcbc3414bdd28a9a8deeb87ccf9e505917b2a855abe5e2",
        "retained": false,
        "external_calls": 0
      }
    },
    "agentcash": {
      "buy": "npx agentcash@latest fetch https://api.delx.ai/api/v1/x402/x402-payment-nonce-check -m POST -H 'x-delx-source: intent-card-x402-payment-nonce-check-api' --max-amount 0.001 -b '{\"nonce\":\"order-42-attempt-1\",\"seen_nonces\":[\"order-41-attempt-1\"],\"minimum_length\":8}'",
      "max_amount_usdc": "0.001"
    }
  },
  "attribution": {
    "header": "x-delx-source",
    "value": "intent-card-x402-payment-nonce-check-api"
  },
  "evidence": {
    "paid_openapi": "https://api.delx.ai/openapi.x402.json",
    "governed_portfolio": "https://api.delx.ai/x402-portfolio.json",
    "live_contract": "https://api.delx.ai/api/v1/x402/x402-payment-nonce-check"
  }
}