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.

A Base pre-confirmation method served on the standard public endpoints (https://mainnet.base.org / https://sepolia.base.org), which are all Flashblocks-enabled.

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 result is a full block object that embeds a calls array alongside the standard block fields:

Field	Type	Description
`number`	string	Simulated block number (hex).
`hash`	string	Simulated block hash.
`parentHash`	string	Parent block hash.
`timestamp`	string	Block timestamp (hex).
`gasLimit`	string	Gas limit (hex).
`gasUsed`	string	Total gas used by the simulated calls (hex).
`baseFeePerGas`	string	Base fee per gas (hex).
`stateRoot`	string	Always `"0x000...000"`, because simulation never commits state to the trie.
`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

curl https://sepolia.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

{
  "jsonrpc": "2.0",
  "id": 1,
  "result": [
    {
      "baseFeePerGas": "0x0",
      "blobGasUsed": "0x39d0",
      "calls": [
        {
          "gasUsed": "0x5208",
          "logs": [],
          "returnData": "0x",
          "status": "0x1"
        }
      ],
      "difficulty": "0x0",
      "excessBlobGas": "0x0",
      "extraData": "0x01000000640000000500000000004c4b40",
      "gasLimit": "0x17d78400",
      "gasUsed": "0x5208",
      "hash": "0x2f2f692821995e39653f63164b2d5d0e0bba66c86c2a199fd3009c0b9906c7b0",
      "logsBloom": "0x000...000",
      "miner": "0x4200000000000000000000000000000000000011",
      "mixHash": "0x0000000000000000000000000000000000000000000000000000000000000000",
      "nonce": "0x0000000000000000",
      "number": "0x2c31c49",
      "parentBeaconBlockRoot": "0x64e625f8bc74f78539f962aa09d522c63576ff6ad57170c668882d99e669ef52",
      "parentHash": "0x9653660afa4fca3976a21d42ebf849c337e9840993f050fee3affc673a573bf8",
      "receiptsRoot": "0xf78dfb743fbd92ade140711c8bbc542b5e307f0ab7984eff35d751969fe57efa",
      "requestsHash": "0xe3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855",
      "sha3Uncles": "0x1dcc4de8dec75d7aab85b567b6ccd41ad312451b948a7413f0a142fd40d49347",
      "size": "0x2a6",
      "stateRoot": "0x0000000000000000000000000000000000000000000000000000000000000000",
      "timestamp": "0x6a10957f",
      "transactions": [
        "0xa401668a06b038c488c1abc013676dfe63fc645d182ece34d8b3f40f45689279"
      ],
      "transactionsRoot": "0x0b1328c457d7a8108ea9f2559142890491b680fdb691720b3d0c857c3d11002c",
      "uncles": [],
      "withdrawals": [],
      "withdrawalsRoot": "0x0000000000000000000000000000000000000000000000000000000000000000"
    }
  ]
}