> ## Documentation Index
> Fetch the complete documentation index at: https://docs.chainstack.com/llms.txt
> Use this file to discover all available pages before exploring further.
# eth_simulateV1 | Monad
> Monad API method that simulates a sequence of calls across one or more blocks with state and block overrides. Reference for eth_simulateV1 on Monad via Chainstack.
Monad API method that simulates a sequence of calls across one or more blocks on top of the state of a chosen block, without creating transactions on the blockchain. Each simulated block can override account state and block fields, and with `traceTransfers` the result reports every native MON transfer as a `Transfer` log.
When called against a block older than the latest \~128 blocks, this method is treated as an archive request (2 RUs instead of 1 RU). See [request units](/docs/request-units#evm-methods-affected-by-block-age).
## Parameters
* `object` — the simulation request object:
* `blockStateCalls` — an array of simulated blocks, executed in order on top of the base block. Each entry contains:
* `blockOverrides` (optional) — block fields to override for this simulated block, such as `number`, `time`, `gasLimit`, or `feeRecipient`.
* `stateOverrides` (optional) — account state to override for the simulation, keyed by address. Each entry can set `balance`, `nonce`, `code`, `state`, or `stateDiff`.
* `calls` — an array of call objects executed in sequence, each with `from`, `to`, and optionally `gas`, `value`, `data`, `nonce`, `maxFeePerGas`, and `maxPriorityFeePerGas`.
* `traceTransfers` (optional) — when `true`, every native MON transfer is returned as a `Transfer` log emitted by `0xeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee`. Defaults to `false`.
* `validation` (optional) — enables transaction checks, such as rejecting a `maxFeePerGas` below the block base fee. Defaults to `true`, and `false` is not supported on Monad.
* `quantity or tag` — the base block: a block number in hex, a block hash, or `latest`, `safe`, `finalized`, or `pending`.
## Response
* `result` — an array with one object per simulated block. Each object contains the block header fields (`number`, `hash`, `parentHash`, `timestamp`, `gasLimit`, `gasUsed`, `baseFeePerGas`, `miner`, `logsBloom`, and the trie roots), `transactions` as an array of transaction hashes, and:
* `calls` — an array with one result per call:
* `status` — `0x1` if the call succeeded, `0x0` if it failed.
* `returnData` — the data returned by the call.
* `gasUsed` — the gas charged for the call. On Monad, this value equals the gas limit of the call.
* `logs` — the logs emitted by the call, including a `Transfer` log for each native MON transfer when `traceTransfers` is `true`.
* `error` — present when the call failed, with a `message` describing the failure.
## Monad-specific behavior
On Monad, `eth_simulateV1` behaves as follows:
* `gasUsed` reports the gas limit of each call, not the gas consumed, because [Monad charges the gas limit](https://docs.monad.xyz/developer-essentials/gas-pricing) of a transaction. A call without `gas` runs with the node's default call gas limit and reports that limit as `gasUsed`. Set `gas` on each call to get a representative value.
* Validation is always on. Omitting `validation` behaves as `true`, and `"validation": false` returns a `-32000` error stating that this mode is not supported yet. Calls without fee fields are accepted.
* The [Monad reserve balance](https://docs.monad.xyz/developer-essentials/reserve-balance) rule applies inside the simulation. A value transfer that leaves the sender below the 10 MON reserve balance reverts with `execution reverted`, except for the sender's first transaction in the reserve window (an emptying transaction). Set the sender's `balance` in `stateOverrides` well above 10 MON when one account makes several value transfers.
* `returnFullTransactions` is not supported. `transactions` always contains transaction hashes.
* The base block must be one whose state the node holds. `earliest` returns the `-32602` error `Block requested not found`.
## Request limits
A single `eth_simulateV1` request on Chainstack Monad nodes accepts:
* Up to 256 simulated blocks in `blockStateCalls`.
* Up to 2,000 calls across all simulated blocks.
* Up to 1,600,000,000 gas in total, summed over the gas limits of all calls. A call without `gas` counts at the node's default call gas limit.
A request over any of these limits returns a `-32000` error that states the limit, for example `Too many calls to simulate: 2001, maximum allowed is 2000`.
## Example: simulate a native MON transfer
The code examples on this page simulate a transfer of 1 MON from `0x5d20879655df3c1e04ab111af0009ad650e762f0` to `0x000000000000000000000000000000000000dEaD` on top of the latest block. The `stateOverrides` entry sets the sender's balance to 100 MON (`0x56bc75e2d63100000`) for the simulation only, so the result does not depend on the account's live balance. The call sets `gas` to 21,000 (`0x5208`), the intrinsic gas of a plain MON transfer.
The simulated call returns `status` `0x1`, `gasUsed` `0x5208`, and one `Transfer` log for the native MON movement:
* `address` — `0xeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee`, the pseudo-address that `traceTransfers` uses for native transfers.
* `topics` — the `Transfer(address,address,uint256)` event signature, then the sender and the recipient.
* `data` — the amount, `1000000000000000000` wei (1 MON).
## `eth_simulateV1` code examples
```javascript ethers.js theme={"system"}
const { JsonRpcProvider } = require("ethers");
const provider = new JsonRpcProvider("CHAINSTACK_NODE_URL");
const sender = "0x5d20879655df3c1e04ab111af0009ad650e762f0";
const recipient = "0x000000000000000000000000000000000000dEaD";
async function simulateTransfer() {
const [block] = await provider.send("eth_simulateV1", [
{
blockStateCalls: [
{
stateOverrides: { [sender]: { balance: "0x56bc75e2d63100000" } }, // 100 MON
calls: [
{
from: sender,
to: recipient,
gas: "0x5208", // 21,000
value: "0xde0b6b3a7640000" // 1 MON
}
]
}
],
traceTransfers: true
},
"latest"
]);
const [result] = block.calls;
console.log(`Simulated block: ${parseInt(block.number, 16)}`);
console.log(`Status: ${result.status}, gas used: ${parseInt(result.gasUsed, 16)}`);
for (const log of result.logs) {
console.log(`Transfer log from ${log.address}: ${BigInt(log.data)} wei`);
}
}
simulateTransfer();
```
```python web3.py theme={"system"}
from web3 import Web3
node_url = "CHAINSTACK_NODE_URL"
web3 = Web3(Web3.HTTPProvider(node_url))
sender = "0x5d20879655df3c1e04ab111af0009ad650e762f0"
recipient = "0x000000000000000000000000000000000000dEaD"
response = web3.provider.make_request("eth_simulateV1", [
{
"blockStateCalls": [
{
"stateOverrides": {sender: {"balance": "0x56bc75e2d63100000"}}, # 100 MON
"calls": [
{
"from": sender,
"to": recipient,
"gas": "0x5208", # 21,000
"value": "0xde0b6b3a7640000" # 1 MON
}
]
}
],
"traceTransfers": True
},
"latest"
])
block = response["result"][0]
result = block["calls"][0]
print(f"Simulated block: {int(block['number'], 16)}")
print(f"Status: {result['status']}, gas used: {int(result['gasUsed'], 16)}")
for log in result["logs"]:
print(f"Transfer log from {log['address']}: {int(log['data'], 16)} wei")
```
## Use case
A practical use case for `eth_simulateV1` is previewing a multi-step flow before signing it, such as a token approval followed by a swap. The calls in one request run in sequence against shared state, so each call sees the effects of the calls before it, and `stateOverrides` funds the sender without touching a real account.
## OpenAPI
````yaml openapi/monad_node_api/execute_transactions/eth_simulateV1.json POST /
openapi: 3.0.0
info:
title: Monad Node API
version: 1.0.0
description: This is an API for interacting with a Monad node.
servers:
- url: https://monad-testnet.core.chainstack.com/9c5b265f20b3ea5df4f54f70eb74b800
security: []
paths:
/:
post:
tags:
- Executing transactions
summary: eth_simulateV1
operationId: eth_simulateV1
requestBody:
required: true
content:
application/json:
schema:
type: object
properties:
id:
type: integer
default: 1
jsonrpc:
type: string
default: '2.0'
method:
type: string
default: eth_simulateV1
params:
type: array
default:
- blockStateCalls:
- stateOverrides:
'0x5d20879655df3c1e04ab111af0009ad650e762f0':
balance: '0x56bc75e2d63100000'
calls:
- from: '0x5d20879655df3c1e04ab111af0009ad650e762f0'
to: '0x000000000000000000000000000000000000dEaD'
gas: '0x5208'
value: '0xde0b6b3a7640000'
traceTransfers: true
- latest
items:
anyOf:
- type: object
title: Simulation config
description: >-
The simulation request: blockStateCalls, and
optionally traceTransfers and validation.
- type: string
title: Block
description: >-
Block number in hex, block hash, or tag (latest, safe,
finalized, pending).
responses:
'200':
description: >-
One object per simulated block, each with the block header fields
and the results of its calls.
content:
application/json:
schema:
type: object
properties:
jsonrpc:
type: string
id:
type: integer
result:
type: array
items:
type: object
properties:
hash:
type: string
parentHash:
type: string
sha3Uncles:
type: string
miner:
type: string
stateRoot:
type: string
transactionsRoot:
type: string
receiptsRoot:
type: string
logsBloom:
type: string
difficulty:
type: string
number:
type: string
gasLimit:
type: string
gasUsed:
type: string
timestamp:
type: string
extraData:
type: string
mixHash:
type: string
nonce:
type: string
baseFeePerGas:
type: string
withdrawalsRoot:
type: string
size:
type: string
uncles:
type: array
items:
type: string
transactions:
type: array
description: Hashes of the simulated transactions.
items:
type: string
withdrawals:
type: array
items:
type: object
calls:
type: array
description: One result per simulated call, in order.
items:
type: object
properties:
status:
type: string
description: 0x1 if the call succeeded, 0x0 if it failed.
returnData:
type: string
description: Data returned by the call.
gasUsed:
type: string
description: >-
Gas charged for the call. On Monad, this
equals the gas limit of the call.
logs:
type: array
description: >-
Logs emitted by the call. With traceTransfers,
native MON transfers appear as Transfer logs
from
0xeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee.
items:
type: object
error:
type: object
description: Present when the call failed.
properties:
message:
type: string
example:
jsonrpc: '2.0'
id: 1
result:
- hash: >-
0x08056c21a4289203c987a823e9f79648efd5014b47b4157a7e3b7a0c751725bd
size: '0x274'
calls:
- logs:
- data: >-
0x0000000000000000000000000000000000000000000000000de0b6b3a7640000
topics:
- >-
0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef
- >-
0x0000000000000000000000005d20879655df3c1e04ab111af0009ad650e762f0
- >-
0x000000000000000000000000000000000000000000000000000000000000dead
address: '0xeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee'
removed: false
logIndex: '0x0'
blockHash: >-
0x08056c21a4289203c987a823e9f79648efd5014b47b4157a7e3b7a0c751725bd
blockNumber: '0x3f04c1c'
transactionHash: >-
0x5e525a3eaa89d73043aa8bc45d09b5b47ee210dc62457f6b0bd41058eb5e118b
transactionIndex: '0x0'
status: '0x1'
gasUsed: '0x5208'
returnData: 0x
miner: '0xa63dd8fc7303bdd6cd66a66a49d4171146f89809'
nonce: '0x0000000000000000'
number: '0x3f04c1c'
uncles: []
gasUsed: '0x5208'
mixHash: >-
0x0000000000000000000000000000000000000000000000000000000000000000
gasLimit: '0x8f0d180'
extraData: 0x
logsBloom: >-
0x00000000000050000000000004000000001000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000008000000000000000000040000000000000000000000000000000000000000000000000000000000000000000000000010000000000000000000000000000004000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000040000000402000000000000000000000000000000000000004000000000000000000000000000000000000000000000000000000000000000000000000000000000
stateRoot: >-
0x56e81f171bcc55a6ff8345e692c0f86e5b48e01b996cadc001622fb5e363b421
timestamp: '0x6ab8d06a'
difficulty: '0x0'
parentHash: >-
0xd0e7e290eab315e8cc182e7aa156d504fb8a1e003abe238be2106a81e1751bc8
sha3Uncles: >-
0x1dcc4de8dec75d7aab85b567b6ccd41ad312451b948a7413f0a142fd40d49347
withdrawals: []
receiptsRoot: >-
0x56e81f171bcc55a6ff8345e692c0f86e5b48e01b996cadc001622fb5e363b421
transactions:
- >-
0x5e525a3eaa89d73043aa8bc45d09b5b47ee210dc62457f6b0bd41058eb5e118b
baseFeePerGas: '0x0'
withdrawalsRoot: >-
0xc5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470
transactionsRoot: >-
0x56e81f171bcc55a6ff8345e692c0f86e5b48e01b996cadc001622fb5e363b421
````