add Quicknode x402 section to data fetching guide

docs/ai-agents/trading/data-fetching.mdx

@@ -1,7 +1,7 @@
 ---
 title: "Fetching Market Data"
-description: "Use x402 to access live market data from CoinGecko, Alchemy, and other sources — no API key management required"
-keywords: ["x402 market data", "trading agent data", "CoinGecko x402", "Alchemy x402", "pay per call data", "agent data fetching"]
+description: "Use x402 to access live market data from CoinGecko, Alchemy, Quicknode, and other sources — no API key management required"
+keywords: ["x402 market data", "trading agent data", "CoinGecko x402", "Alchemy x402", "Quicknode x402", "pay per call data", "agent data fetching"]
 ---
 
 import { DataFetchingDemo } from "/snippets/DataFetchingDemo.jsx"
@@ -145,6 +145,96 @@ PAYMENT_SIG=$(npx @alchemy/x402 pay --private-key ./wallet-key.txt --payment-req
 
 See the full [Alchemy Agentic Gateway skill](https://github.com/alchemyplatform/skills/tree/main/skills/agentic-gateway) for wallet bootstrap, payment handling, and SDK integration.
 
+### Quicknode — onchain data
+
+Quicknode's x402 gateway at `https://x402.quicknode.com` gives your agent direct RPC access to Base (mainnet and Sepolia) without an account or API key. Pay per request in USDC, or buy credits in bulk if you're making a lot of calls.
+
+<Note>
+  What sets Quicknode apart from other x402 providers: three payment tiers (per-request at `$0.001`, nanopayments at `$0.0001` via Circle Gateway, and credit drawdown for bulk use), WebSocket connections for streaming Base data, and a built-in Base Sepolia faucet so you can start testing without sourcing testnet USDC elsewhere.
+</Note>
+
+Fetch token balances on Base:
+
+<Tabs>
+  <Tab title="Per-request (curl)">
+    ```bash Terminal
+    # Read USDC balance for an address on Base
+    # balanceOf(address) selector: 0x70a08231
+    curl -X POST "https://x402.quicknode.com/base-mainnet" \
+      -H "Content-Type: application/json" \
+      -d '{
+        "jsonrpc": "2.0",
+        "id": 1,
+        "method": "eth_call",
+        "params": [{
+          "to": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
+          "data": "0x70a08231000000000000000000000000YOUR_ADDRESS_HERE"
+        }, "latest"]
+      }'
+    ```
+
+    If the endpoint returns `402`, sign the EIP-712 payment payload from the response body and include it as a `PAYMENT-SIGNATURE` header on retry. Each call costs `$0.001` USDC. Failed requests and JSON-RPC errors don't cost anything, so you only pay when you actually get data back.
+  </Tab>
+  <Tab title="Nanopayment (Circle Gateway)">
+    Nanopayments run `$0.0001` per call, 10x cheaper than per-request. They require a Circle Gateway Wallet deposit and are available on Base Sepolia for now.
+
+    ```bash Terminal
+    # Read USDC balance for an address on Base Sepolia
+    # balanceOf(address) selector: 0x70a08231
+    curl -X POST "https://x402.quicknode.com/base-sepolia" \
+      -H "Content-Type: application/json" \
+      -d '{
+        "jsonrpc": "2.0",
+        "id": 1,
+        "method": "eth_call",
+        "params": [{
+          "to": "0x036CbD53842c5426634e7929541eC2318f3dCF7e",
+          "data": "0x70a08231000000000000000000000000YOUR_ADDRESS_HERE"
+        }, "latest"]
+      }'
+    ```
+
+    When you get the `402` back, find the `accepts` entry where `extra.name` is `"GatewayWalletBatched"`, sign it, and send it as the `PAYMENT-SIGNATURE` header on retry. Testnet cap is 10,000 requests (about `$1` total).
+  </Tab>
+  <Tab title="Credit drawdown (authenticated)">
+    For high-volume use, authenticate with SIWX and pay with credits instead:
+
+    ```bash Terminal
+    # 1. Sign in with your wallet (SIWX)
+    curl -X POST "https://x402.quicknode.com/auth" \
+      -H "Content-Type: application/json" \
+      -d '{
+        "message": "<your-siwx-message>",
+        "signature": "<your-signature>",
+        "type": "siwx"
+      }'
+
+    # 2. Read USDC balance using the JWT
+    # balanceOf(address) selector: 0x70a08231
+    curl -X POST "https://x402.quicknode.com/base-mainnet" \
+      -H "Content-Type: application/json" \
+      -H "Authorization: Bearer <jwt-token>" \
+      -d '{
+        "jsonrpc": "2.0",
+        "id": 1,
+        "method": "eth_call",
+        "params": [{
+          "to": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
+          "data": "0x70a08231000000000000000000000000YOUR_ADDRESS_HERE"
+        }, "latest"]
+      }'
+    ```
+
+    Credits cost `$10` per 1,000,000 on mainnet. You only get charged for successful responses.
+  </Tab>
+</Tabs>
+
+If you're building a TypeScript agent, the [`@quicknode/x402`](https://www.npmjs.com/package/@quicknode/x402) SDK handles auth, payment signing, JWT management, and WebSocket connections so you don't have to wire up the 402 flow manually.
+
+<Tip>
+  Quicknode includes a testnet faucet on Base Sepolia. After authenticating, call `POST /drip` to get free USDC for testing. No external faucet needed.
+</Tip>
+
 ## Making data calls inside an OpenClaw agent
 
 Install the [Sponge Wallet](https://www.paysponge.com) skill or [CDP Agentic Wallet](https://docs.cdp.coinbase.com/agentic-wallet/) skills, then prompt your agent directly: