# eth\_simulateV1

Simulates one or more transaction bundles against the current preconfirmed Flashblock state.

This method supports state overrides, block overrides, multi-block simulation, and optional ETH transfer tracing.\
\
This method will use `40` [Compute Units](https://docs.validationcloud.io/v1/about/billing).

***

### Parameters:

`params` - array containing:

1. `simulationPayload` — object - required

Configuration object for the simulation.

#### **simulationPayload fields:**

* `blockStateCalls` — array - required\
  Array of block simulation objects. Each represents a simulated block.
* `traceTransfers` — boolean - optional\
  If `true`, ETH transfers are included as logs. Defaults to `false`.
* `validation` — boolean - optional\
  If `true`, applies validation checks such as nonce and balance. Defaults to `false`.

#### **blockStateCalls object fields:**

* `calls` — array\
  List of transaction call objects to simulate
* `stateOverrides` — object - optional\
  Override account state (balance, nonce, code, storage)
* `blockOverrides` — object - optional\
  Override block-level fields (e.g. `number`, `timestamp`, `baseFeePerGas`)

#### **call object fields:**

* `from` — string - optional\
  Sender address
* `to` — string\
  Recipient address
* `maxFeePerGas` — string - optional\
  Max fee per gas (hex)
* `value` — string - optional\
  ETH value sent (hex)
* `data` — string - optional\
  Hex-encoded calldata

2. `blockParameter` — string - required

Block number, hash, or tag.

Use `"pending"` to simulate against the latest Flashblock state.

### Returns:

`array of objects` - simulated block results

Each object represents one simulated block.

#### **Block result fields:**

* `number` — string\
  Block number (hex)
* `hash` — string\
  Block hash
* `gasUsed` — string\
  Total gas used (hex)
* `baseFeePerGas` — string\
  Base fee (hex)
* `calls` — array\
  Results of each simulated call

#### **Call result fields:**

* `status` — string\
  "0x1" = success, "0x0" = failure
* `gasUsed` — string\
  Gas used (hex)
* `returnData` — string\
  Return data (hex)
* `logs` — array\
  Emitted logs (includes transfers if enabled)
* `error` — string\
  Error or revert reason (if failed)

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

### Example Request

{% tabs %}
{% tab title="mainnet" %}

```bash
curl https://mainnet.base.validationcloud.io/v1/<YOUR_API_KEY_HERE> \
  -X POST \
  -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
      },
      "pending"
    ],
    "id": 1
  }'
```

{% endtab %}

{% tab title="testnet" %}

```bash
curl https://sepolia.base.validationcloud.io/v1/<YOUR_API_KEY_HERE> \
  -X POST \
  -H "Content-Type: application/json" \
  -d '{
    "jsonrpc": "2.0",
    "method": "eth_simulateV1",
    "params": [
      {
        "blockStateCalls": [
          {
            "calls": [
              {
                "to": "0x...",
                "data": "0x..."
              }
            ],
            "stateOverrides": {}
          }
        ],
        "traceTransfers": true,
        "validation": true
      },
      "pending"
    ],
    "id": 1
  }'
```

{% endtab %}
{% endtabs %}