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

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

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