eth_simulateV1

Simulates one or more transaction bundles against Base state, including Flashblocks preconfirmed state. Returns simulated block results with call status, gas used, return data, logs, and errors — without broadcasting anything onchain.

Use Cases

• Transaction preview — Verify a swap or transfer will succeed before sending
• Multi-call simulation — Simulate a sequence of dependent transactions atomically
• State override testing — Override account balances or contract storage for what-if analysis
• Gas estimation — Get precise gas usage for complex call sequences

Parameters

Parameter	Type	Required	Description
simulatePayload	Object	Yes	Object containing blockStateCalls, traceTransfers, and validation
blockTag	QUANTITY|TAG	Yes	Block number in hex, or "latest", "pending"

simulatePayload Fields

Field	Type	Description
blockStateCalls	Array	Array of block objects, each containing calls (array of transaction objects), optional stateOverrides, and optional blockOverrides
traceTransfers	Boolean	If true, trace ETH transfers during simulation
validation	Boolean	If true, run additional validation checks

Request

{
  "jsonrpc": "2.0",
  "method": "eth_simulateV1",
  "params": [
    {
      "blockStateCalls": [
        {
          "calls": [
            {
              "from": "0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045",
              "to": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
              "data": "0x70a08231000000000000000000000000d8dA6BF26964aF9D7eEd9e03E53415D37aA96045"
            }
          ]
        }
      ],
      "traceTransfers": true,
      "validation": false
    },
    "latest"
  ],
  "id": 1
}

Returns

An array of simulated block results, each containing:

Field	Type	Description
number	QUANTITY	Simulated block number
hash	DATA	Simulated block hash
gasUsed	QUANTITY	Total gas used
calls	Array	Array of call results

Call Result Fields

Field	Type	Description
status	QUANTITY	0x1 for success, 0x0 for revert
returnData	DATA	ABI-encoded return data
gasUsed	QUANTITY	Gas consumed by this call
logs	Array	Logs emitted during simulation
error	Object	Error details if call reverted

Code Examples

cURL

curl -X POST https://api-base-mainnet-archive.n.dwellir.com/YOUR_API_KEY \
  -H "Content-Type: application/json" \
  -d '{
    "jsonrpc": "2.0",
    "method": "eth_simulateV1",
    "params": [
      {
        "blockStateCalls": [
          {
            "calls": [
              {
                "from": "0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045",
                "to": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
                "data": "0x70a08231000000000000000000000000d8dA6BF26964aF9D7eEd9e03E53415D37aA96045"
              }
            ]
          }
        ],
        "traceTransfers": true,
        "validation": false
      },
      "latest"
    ],
    "id": 1
  }'

JavaScript

const response = await fetch(
  'https://api-base-mainnet-archive.n.dwellir.com/YOUR_API_KEY',
  {
    method: 'POST',
    headers: { 'Content-Type': 'application/json' },
    body: JSON.stringify({
      jsonrpc: '2.0',
      method: 'eth_simulateV1',
      params: [
        {
          blockStateCalls: [
            {
              calls: [
                {
                  from: '0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045',
                  to: '0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913',
                  data: '0x70a08231000000000000000000000000d8dA6BF26964aF9D7eEd9e03E53415D37aA96045',
                },
              ],
            },
          ],
          traceTransfers: true,
          validation: false,
        },
        'latest',
      ],
      id: 1,
    }),
  }
);

const data = await response.json();
for (const block of data.result) {
  for (const call of block.calls) {
    console.log('Status:', call.status === '0x1' ? 'success' : 'reverted');
    console.log('Gas used:', parseInt(call.gasUsed, 16));
    console.log('Return data:', call.returnData);
  }
}

Python

import requests

response = requests.post(
    'https://api-base-mainnet-archive.n.dwellir.com/YOUR_API_KEY',
    json={
        'jsonrpc': '2.0',
        'method': 'eth_simulateV1',
        'params': [
            {
                'blockStateCalls': [
                    {
                        'calls': [
                            {
                                'from': '0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045',
                                'to': '0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913',
                                'data': '0x70a08231000000000000000000000000d8dA6BF26964aF9D7eEd9e03E53415D37aA96045'
                            }
                        ]
                    }
                ],
                'traceTransfers': True,
                'validation': False
            },
            'latest'
        ],
        'id': 1
    }
)

result = response.json()['result']
for block in result:
    for call in block['calls']:
        print(f"Status: {'success' if call['status'] == '0x1' else 'reverted'}")
        print(f"Gas used: {int(call['gasUsed'], 16)}")
        print(f"Return data: {call['returnData']}")

Response Example

{
  "jsonrpc": "2.0",
  "id": 1,
  "result": [
    {
      "number": "0x29442bb",
      "hash": "0xcefc6e6e...",
      "gasUsed": "0x79ce",
      "calls": [
        {
          "returnData": "0x00000000000000000000000000000000000000000000000000000000011420f9",
          "logs": [],
          "gasUsed": "0x79ce",
          "status": "0x1"
        }
      ]
    }
  ]
}

Error Handling

Error Code	Message	Description
-32602	Invalid params	Malformed simulation payload
-32000	Execution reverted	One or more simulated calls reverted

Related Methods

• eth_call — Execute a single read-only call
• eth_estimateGas — Estimate gas for a transaction
• eth_sendRawTransactionSync — Send a transaction and wait for Flashblock inclusion

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Need help? Contact our support team or check the Base documentation.