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This guide walks through the core Shield workflow: simulate a transaction to predict its outcome, then validate it before signing. We’ll use a simple ETH → WETH wrap as the example transaction — the calldata is just 0xd0e30db0 (the deposit() function selector), so you can copy-paste and run immediately.

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Prerequisites

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1. Simulate a Transaction

Send your transaction to the simulate endpoint to get predicted output amounts and gas consumption. 
curl -X POST https://shield.api.enso.build/api/v1/simulate \
  -H "Authorization: Bearer $ENSO_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "chainId": 1,
    "transaction": {
      "data": "0xd0e30db0",
      "value": "1000000000000000000",
      "to": "0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2",
      "from": "0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045"
    },
    "tokenIn": ["0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE"],
    "tokenOut": ["0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2"],
    "amountIn": ["1000000000000000000"]
  }'
Response: 
{
  "simulationId": "a1b2c3d4-e5f6-7890-abcd-ef1234567890",
  "chainId": 1,
  "result": {
    "status": "Success",
    "amountOut": ["1000000000000000000"],
    "gas": "46000"
  }
}
The simulationId is a UUID you’ll use in the next step to validate the transaction before signing.

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2. Validate Before Signing

Before signing the transaction, send it with the simulationId to confirm nothing has changed. 
curl -X POST https://shield.api.enso.build/api/v1/validate \
  -H "Authorization: Bearer $ENSO_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "simulationId": "<SIMULATION_ID>",
    "transaction": {
      "data": "0xd0e30db0",
      "to": "0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2",
      "from": "0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045",
      "value": "1000000000000000000",
      "chainId": 1
    }
  }'
Response: 
{
  "valid": true,
  "simulationId": "a1b2c3d4-e5f6-7890-abcd-ef1234567890",
  "checks": {
    "chainId": true,
    "data": true,
    "to": true,
    "value": true,
    "from": true
  }
}

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3. Sign and Submit

Once validated, sign and submit the transaction using any web3 library. 
import { createWalletClient, http } from "viem";
import { mainnet } from "viem/chains";
import { privateKeyToAccount } from "viem/accounts";

const account = privateKeyToAccount("0x...");
const client = createWalletClient({ account, chain: mainnet, transport: http() });

if (validation.valid) {
  const hash = await client.sendTransaction({
    to: "0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2",
    data: "0xd0e30db0",
    value: BigInt("1000000000000000000"),
  });
  console.log("Transaction hash:", hash);
}
Simulations are cached for 5 minutes. Validate within this window, or re-simulate to get a fresh simulationId.
Shield works with transactions from any source — Uniswap, Enso, Aave, or your own contracts. See the Third-Party Transactions guide for examples.

Updated