---
title: "eth_simulateV1"
description: "Simulates one or more transaction bundles against the current pre-confirmed Flashblock state, with state overrides and optional transfer tracing."
source: https://basehub.org/api-reference/flashblocks/eth_simulatev1/
---
Simulates one or more transaction bundles against the current pre-confirmed Flashblock state. Supports state overrides, multi-block simulation, and optional transfer tracing.

Only available on Flashblocks endpoints: `https://mainnet-preconf.base.org` / `https://sepolia-preconf.base.org`.

## Parameters

| Name | Type | Required | Description |
| --- | --- | --- | --- |
| `simulationPayload` | object | Yes | The simulation configuration. |
| `blockParameter` | string | Yes | Use `"pending"` to simulate against the current Flashblock state. |

The `simulationPayload` object accepts:

| Field | Type | Required | Description |
| --- | --- | --- | --- |
| `blockStateCalls` | array | Yes | Array of block state call objects. Each object represents one simulated block. |
| `traceTransfers` | boolean | No | If `true`, ETH transfer events are included as logs in the result. Defaults to `false`. |
| `validation` | boolean | No | If `true`, transaction validation (nonce, balance) is enforced. Defaults to `false`. |

Each entry in `blockStateCalls` accepts:

| Field | Type | Description |
| --- | --- | --- |
| `calls` | array | Array of transaction call objects to simulate within this block. |
| `stateOverrides` | object | Per-address state overrides applied before simulation (for example, balance, nonce, code, storage). Optional. |
| `blockOverrides` | object | Block-level overrides (for example, `number`, `timestamp`). Optional. |

## Returns

`result` is an array of simulated block results, one per entry in `blockStateCalls`. Each block result has:

| Field | Type | Description |
| --- | --- | --- |
| `calls` | array | Array of individual call results. |

Each entry in `calls` has:

| Field | Type | Description |
| --- | --- | --- |
| `status` | string | `"0x1"` for success, `"0x0"` for failure. |
| `gasUsed` | string | Gas used as a hexadecimal integer. |
| `returnData` | string | Hex-encoded return data. |
| `logs` | array | Logs emitted (including ETH transfer logs if `traceTransfers` is `true`). |
| `error` | string | Revert reason if the call failed. Optional. |

## Example

### Request

```bash
curl https://sepolia-preconf.base.org \
  -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
  }'
```

### Response

```json
{
  "jsonrpc": "2.0",
  "id": 1,
  "result": [
    {
      "calls": [
        {
          "status": "0x1",
          "gasUsed": "0x5208",
          "returnData": "0x",
          "logs": []
        }
      ]
    }
  ]
}
```