Pre-flight / preview
Transaction Preview is an extension of our Transaction Simulation Platform for on-demand simulations of unsigned transactions against the current block height.
Transaction Preview lets you preview the outputs of any custom transactions that you submit to it. By harnessing the power of our network of Ethereum nodes, with our existing decoding and transaction lifecycle knowledge, we hope to give users of Transaction Preview even greater comfort when interacting in the Web3 space. Previewing a transaction is particularly useful for:
- Wallets: Help users preview net-balance changes & identify malicious contract behavior or buggy smart contracts before interacting with them.
- DEXs & Swaps: Report accurate slippage, Accurate tokens received, and accurate failing calls
- Traders: Preview many iterations of the same trade and execute only the most profitable one
- Lending Protocols: Tell whether a Borrow / Repay / Claim transaction will go through
- Auctions: Tell whether your bid or listing will go through and its accuracy & effects
- NFTs: Tell whether your NFT mint, purchase, or transfer will go through
& much more without spending a single wei in gas!
Transaction Preview comes in the form of both REST and Websocket endpoints, to which you can outline the basics of a single or multiple transactions, and you will receive a payload detailing the execution of the transactions in the latest block height. We simulate the proposed transactions by executing it on one of our dedicated simulator nodes on the current block height. The returned payload includes:
- 1.Any EVM execution errors
- 2.A list of Decoded Internal Transactions
- 3.A collection of all balance changes of tokens across all involved addresses
- 4.End to end performance metrics of the simulation
Make sure to enter your own api key and secret
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This example request simulates a single transaction : Vitalik swapping Eth for Dai on Sushiswap with a deadline of Fri Jan 15 2027
curl --location --request POST 'https://api.blocknative.com/simulate' \
--header 'credentials: <api-key>:<secret>' \
--header 'Content-Type: application/json' \
--data-raw '{
"system":"ethereum",
"network":"main",
"transactions":[{
"to":"0xd9e1cE17f2641f24aE83637ab66a2cca9C378B9F",
"from":"0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045",
"gas":10407056,
"maxFeePerGas":102306635634,
"maxPriorityFeePerGas":2.14,
"value":100000000000000000,
"input":"0x7ff36ab500000000000000000000000000000000000000000000000fc7fc9610eacf03cd0000000000000000000000000000000000000000000000000000000000000080000000000000000000000000d8dA6BF26964aF9D7eEd9e03E53415D37aA96045000000000000000000000000000000000000000000000000000665178b034cc90000000000000000000000000000000000000000000000000000000000000002000000000000000000000000c02aaa39b223fe8d0a0e5c4f27ead9083c756cc20000000000000000000000006b175474e89094c44da98b954eedeac495271d0f"
}
]
}'
{
"status": "simulated",
"simulatedBlockNumber": 14674533,
"transactions": [
{
"from": "0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045",
"to": "0xd9e1cE17f2641f24aE83637ab66a2cca9C378B9F",
"value": 100000000000000000,
"gas": 10407056,
"input": "0x7ff36ab500000000000000000000000000000000000000000000000fc7fc9610eacf03cd0000000000000000000000000000000000000000000000000000000000000080000000000000000000000000d8dA6BF26964aF9D7eEd9e03E53415D37aA96045000000000000000000000000000000000000000000000000000665178b034cc90000000000000000000000000000000000000000000000000000000000000002000000000000000000000000c02aaa39b223fe8d0a0e5c4f27ead9083c756cc20000000000000000000000006b175474e89094c44da98b954eedeac495271d0f",
"type": 2,
"maxFeePerGas": 102306635634,
"maxPriorityFeePerGas": 2.14
}
],
"internalTransactions": [
[
{
"type": "CALL",
"from": "0xd9e1ce17f2641f24ae83637ab66a2cca9c378b9f",
"to": "0xc02aaa39b223fe8d0a0e5c4f27ead9083c756cc2",
"input": "0xd0e30db0",
"gas": 10203912,
"gasUsed": 23974,
"value": "100000000000000000"
},
{
"type": "CALL",
"from": "0xd9e1ce17f2641f24ae83637ab66a2cca9c378b9f",
"to": "0xc02aaa39b223fe8d0a0e5c4f27ead9083c756cc2",
"input": "0xa9059cbb000000000000000000000000c3d03e4f041fd4cd388c549ee2a29a9e5075882f000000000000000000000000000000000000000000000000016345785d8a0000",
"gas": 10178983,
"gasUsed": 8062,
"value": "0",
"contractCall": {
"methodName": "transfer",
"params": {
"_to": "0xc3d03e4f041fd4cd388c549ee2a29a9e5075882f",
"_value": "100000000000000000"
},
"contractAddress": "0xc02aaa39b223fe8d0a0e5c4f27ead9083c756cc2",
"contractType": "erc20",
"contractAlias": "WETH",
"contractDecimals": 18,
"contractName": "Wrapped Ether",
"decimalValue": "0.1"
}
},
{
"type": "CALL",
"from": "0xd9e1ce17f2641f24ae83637ab66a2cca9c378b9f",
"to": "0xc3d03e4f041fd4cd388c549ee2a29a9e5075882f",
"input": "0x022c0d9f00000000000000000000000000000000000000000000000ff0aa8d89e86502cb0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000d8da6bf26964af9d7eed9e03e53415d37aa9604500000000000000000000000000000000000000000000000000000000000000800000000000000000000000000000000000000000000000000000000000000000",
"gas": 10168823,
"gasUsed": 48406,
"value": "0"
},
{
"type": "CALL",
"from": "0xc3d03e4f041fd4cd388c549ee2a29a9e5075882f",
"to": "0x6b175474e89094c44da98b954eedeac495271d0f",
"input": "0xa9059cbb000000000000000000000000d8da6bf26964af9d7eed9e03e53415d37aa9604500000000000000000000000000000000000000000000000ff0aa8d89e86502cb",
"gas": 9996662,
"gasUsed": 13074,
"value": "0",
"contractCall": {
"methodName": "transfer",
"params": {
"_to": "0xd8da6bf26964af9d7eed9e03e53415d37aa96045",
"_value": "294042990044235760331"
},
"contractAddress": "0x6b175474e89094c44da98b954eedeac495271d0f",
"contractType": "erc20",
"contractAlias": "DAI",
"contractDecimals": 18,
"contractName": "Dai Stablecoin",
"decimalValue": "294.042990044235760331"
}
}
]
],
"netBalanceChanges": [
[
{
"address": "0xd9e1ce17f2641f24ae83637ab66a2cca9c378b9f",
"balanceChanges": [
{
"delta": "-100000000000000000",
"asset": {
"type": "ether",
"symbol": "ETH"
},
"breakdown": [
{
"counterparty": "0xc02aaa39b223fe8d0a0e5c4f27ead9083c756cc2",
"amount": "-100000000000000000"
}
]
},
{
"delta": "-100000000000000000",
"asset": {
"type": "erc20",
"symbol": "WETH",
"contractAddress": "0xc02aaa39b223fe8d0a0e5c4f27ead9083c756cc2"
},
"breakdown": [
{
"counterparty": "0xc3d03e4f041fd4cd388c549ee2a29a9e5075882f",
"amount": "-100000000000000000"
}
]
}
]
},
{
"address": "0xc02aaa39b223fe8d0a0e5c4f27ead9083c756cc2",
"balanceChanges": [
{
"delta": "100000000000000000",
"asset": {
"type": "ether",
"symbol": "ETH"
},
"breakdown": [
{
"counterparty": "0xd9e1ce17f2641f24ae83637ab66a2cca9c378b9f",
"amount": "100000000000000000"
}
]
}
]
},
{
"address": "0xc3d03e4f041fd4cd388c549ee2a29a9e5075882f",
"balanceChanges": [
{
"delta": "100000000000000000",
"asset": {
"type": "erc20",
"symbol": "WETH",
"contractAddress": "0xc02aaa39b223fe8d0a0e5c4f27ead9083c756cc2"
},
"breakdown": [
{
"counterparty": "0xd9e1ce17f2641f24ae83637ab66a2cca9c378b9f",
"amount": "100000000000000000"
}
]
},
{
"delta": "-294042990044235760331",
"asset": {
"type": "erc20",
"symbol": "DAI",
"contractAddress": "0x6b175474e89094c44da98b954eedeac495271d0f"
},
"breakdown": [
{
"counterparty": "0xd8da6bf26964af9d7eed9e03e53415d37aa96045",
"amount": "-294042990044235760331"
}
]
}
]
},
{
"address": "0xd8da6bf26964af9d7eed9e03e53415d37aa96045",
"balanceChanges": [
{
"delta": "294042990044235760331",
"asset": {
"type": "erc20",
"symbol": "DAI",
"contractAddress": "0x6b175474e89094c44da98b954eedeac495271d0f"
},
"breakdown": [
{
"counterparty": "0xc3d03e4f041fd4cd388c549ee2a29a9e5075882f",
"amount": "294042990044235760331"
}
]
}
]
}
]
],
"error": [],
"simDetails": {
"blockNumber": -1,
"performanceProfile": {
"breakdown": [
{
"label": "detected",
"timeStamp": "2022-04-28T17:37:18.993Z"
},
{
"label": "traceStart",
"timeStamp": "2022-04-28T17:37:18.994Z"
},
{
"label": "traceEnd",
"timeStamp": "2022-04-28T17:37:19.024Z"
},
{
"label": "dispatch",
"timeStamp": "2022-04-28T17:37:19.025Z"
}
]
},
"e2eMs": 32
},
"serverVersion": "0.133.0-0.4.8",
"system": "ethereum",
"network": "main",
"contractCall": [
{
"status": "fulfilled",
"value": {
"methodName": "swapExactETHForTokens",
"params": {
"amountOutMin": "291111719012725097421",
"deadline": "1800001651166409",
"path": [
"0xc02aaa39b223fe8d0a0e5c4f27ead9083c756cc2",
"0x6b175474e89094c44da98b954eedeac495271d0f"
],
"to": "0xd8da6bf26964af9d7eed9e03e53415d37aa96045"
},
"contractAddress": "0xd9e1cE17f2641f24aE83637ab66a2cca9C378B9F"
}
}
]
}
post
https://api.blocknative.com
/simulate
Endpoint Spec
This payload will simulate Vitalik approving Sushiswap to transfer Balancer tokens, and then swaps Balancer for DAI on Sushiswap.
curl --location --request POST 'https://api.blocknative.com/simulate' \
--header 'credentials: <api-key>:<secret>' \
--header 'Content-Type: application/json' \
--data-raw '{
"system":"ethereum",
"network":"main",
"transactions":[
{
"to":"0xba100000625a3754423978a60c9317c58a424e3D",
"from":"0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045",
"gas":12407056,
"maxFeePerGas":82306635634,
"maxPriorityFeePerGas":2.14,
"value":0,
"input":"0x095ea7b3000000000000000000000000d9e1cE17f2641f24aE83637ab66a2cca9C378B9F000000000000000000000000000000000785ee10d5da46d900f436a000000000"
},
{
"to":"0xd9e1cE17f2641f24aE83637ab66a2cca9C378B9F",
"from":"0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045",
"gas":10407056,
"maxFeePerGas":102306635634,
"maxPriorityFeePerGas":2.14,
"value":0,
"input":"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"
}
]
}'
{
"status": "simulated",
"simulatedBlockNumber": 14674533,
"transactions": [
{
"from": "0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045",
"to": "0xba100000625a3754423978a60c9317c58a424e3D",
"value": 0,
"gas": 12407056,
"input": "0x095ea7b3000000000000000000000000d9e1cE17f2641f24aE83637ab66a2cca9C378B9F000000000000000000000000000000000785ee10d5da46d900f436a000000000",
"type": 2,
"maxFeePerGas": 82306635634,
"maxPriorityFeePerGas": 2.14
},
{
"from": "0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045",
"to": "0xd9e1cE17f2641f24aE83637ab66a2cca9C378B9F",
"value": 0,
"gas": 10407056,
"input": "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",
"type": 2,
"maxFeePerGas": 102306635634,
"maxPriorityFeePerGas": 2.14
}
],
"internalTransactions": [
[],
[
{
"type": "CALL",
"from": "0xd9e1ce17f2641f24ae83637ab66a2cca9c378b9f",
"to": "0xba100000625a3754423978a60c9317c58a424e3d",
"input": "0x23b872dd000000000000000000000000d8da6bf26964af9d7eed9e03e53415d37aa960450000000000000000000000009bffa3ce3e56d0d26447a45771fec76bd4173022000000000000000000000000000000000000000000000000016345785d8a0000",
"gas": 10201236,
"gasUsed": 25509,
"value": "0",
"contractCall": {
"methodName": "transferFrom",
"params": {
"amount": "100000000000000000",
"recipient": "0x9bffa3ce3e56d0d26447a45771fec76bd4173022",
"sender": "0xd8da6bf26964af9d7eed9e03e53415d37aa96045"
},
"contractAddress": "0xba100000625a3754423978a60c9317c58a424e3d",
"contractType": "Balancer: BAL Token"
}
},
{
"type": "CALL",
"from": "0xd9e1ce17f2641f24ae83637ab66a2cca9c378b9f",
"to": "0x9bffa3ce3e56d0d26447a45771fec76bd4173022",
"input": "0x022c0d9f00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000001c0c6cf1cacf1000000000000000000000000c3d03e4f041fd4cd388c549ee2a29a9e5075882f00000000000000000000000000000000000000000000000000000000000000800000000000000000000000000000000000000000000000000000000000000000",
"gas": 10172992,
"gasUsed": 48134,
"value": "0"
},
{
"type": "CALL",
"from": "0x9bffa3ce3e56d0d26447a45771fec76bd4173022",
"to": "0xc02aaa39b223fe8d0a0e5c4f27ead9083c756cc2",
"input": "0xa9059cbb000000000000000000000000c3d03e4f041fd4cd388c549ee2a29a9e5075882f0000000000000000000000000000000000000000000000000001c0c6cf1cacf1",
"gas": 10000736,
"gasUsed": 12862,
"value": "0",
"contractCall": {
"methodName": "transfer",
"params": {
"_to": "0xc3d03e4f041fd4cd388c549ee2a29a9e5075882f",
"_value": "493435087531249"
},
"contractAddress": "0xc02aaa39b223fe8d0a0e5c4f27ead9083c756cc2",
"contractType": "erc20",
"contractAlias": "WETH",
"contractDecimals": 18,
"contractName": "Wrapped Ether",
"decimalValue": "0.000493435087531249"
}
},
{
"type": "CALL",
"from": "0xd9e1ce17f2641f24ae83637ab66a2cca9c378b9f",
"to": "0xc3d03e4f041fd4cd388c549ee2a29a9e5075882f",
"input": "0x022c0d9f000000000000000000000000000000000000000000000000143f3a1695d5a8dc0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000d8da6bf26964af9d7eed9e03e53415d37aa9604500000000000000000000000000000000000000000000000000000000000000800000000000000000000000000000000000000000000000000000000000000000",
"gas": 10123578,
"gasUsed": 48406,
"value": "0"
},
{
"type": "CALL",
"from": "0xc3d03e4f041fd4cd388c549ee2a29a9e5075882f",
"to": "0x6b175474e89094c44da98b954eedeac495271d0f",
"input": "0xa9059cbb000000000000000000000000d8da6bf26964af9d7eed9e03e53415d37aa96045000000000000000000000000000000000000000000000000143f3a1695d5a8dc",
"gas": 9952124,
"gasUsed": 13074,
"value": "0",
"contractCall": {
"methodName": "transfer",
"params": {
"_to": "0xd8da6bf26964af9d7eed9e03e53415d37aa96045",
"_value": "1458948672968829148"
},
"contractAddress": "0x6b175474e89094c44da98b954eedeac495271d0f",
"contractType": "erc20",
"contractAlias": "DAI",
"contractDecimals": 18,
"contractName": "Dai Stablecoin",
"decimalValue": "1.458948672968829148"
}
}
]
],
"netBalanceChanges": [
[],
[
{
"address": "0x9bffa3ce3e56d0d26447a45771fec76bd4173022",
"balanceChanges": [
{
"delta": "-493435087531249",
"asset": {
"type": "erc20",
"symbol": "WETH",
"contractAddress": "0xc02aaa39b223fe8d0a0e5c4f27ead9083c756cc2"
},
"breakdown": [
{
"counterparty": "0xc3d03e4f041fd4cd388c549ee2a29a9e5075882f",
"amount": "-493435087531249"
}
]
}
]
},
{
"address": "0xc3d03e4f041fd4cd388c549ee2a29a9e5075882f",
"balanceChanges": [
{
"delta": "493435087531249",
"asset": {
"type": "erc20",
"symbol": "WETH",
"contractAddress": "0xc02aaa39b223fe8d0a0e5c4f27ead9083c756cc2"
},
"breakdown": [
{
"counterparty": "0x9bffa3ce3e56d0d26447a45771fec76bd4173022",
"amount": "493435087531249"
}
]
},
{
"delta": "-1458948672968829148",
"asset": {
"type": "erc20",
"symbol": "DAI",
"contractAddress": "0x6b175474e89094c44da98b954eedeac495271d0f"
},
"breakdown": [
{
"counterparty": "0xd8da6bf26964af9d7eed9e03e53415d37aa96045",
"amount": "-1458948672968829148"
}
]
}
]
},
{
"address": "0xd8da6bf26964af9d7eed9e03e53415d37aa96045",
"balanceChanges": [
{
"delta": "1458948672968829148",
"asset": {
"type": "erc20",
"symbol": "DAI",
"contractAddress": "0x6b175474e89094c44da98b954eedeac495271d0f"
},
"breakdown": [
{
"counterparty": "0xc3d03e4f041fd4cd388c549ee2a29a9e5075882f",
"amount": "1458948672968829148"
}
]
}
]
}
]
],
"error": [],
"simDetails": {
"blockNumber": -1,
"performanceProfile": {
"breakdown": [
{
"label": "detected",
"timeStamp": "2022-04-28T18:18:42.893Z"
},
{
"label": "traceStart",
"timeStamp": "2022-04-28T18:18:42.896Z"
},
{
"label": "traceEnd",
"timeStamp": "2022-04-28T18:18:42.929Z"
},
{
"label": "dispatch",
"timeStamp": "2022-04-28T18:18:42.929Z"
}
]
},
"e2eMs": 36
},
"serverVersion": "0.133.0-0.4.8",
"system": "ethereum",
"network": "main",
"contractCall": [
{
"status": "fulfilled",
"value": {
"methodName": "approve",
"params": {
"amount": "10000000000000000000000000000000000000",
"spender": "0xd9e1ce17f2641f24ae83637ab66a2cca9c378b9f"
},
"contractAddress": "0xba100000625a3754423978a60c9317c58a424e3D",
"contractType": "erc20",
"contractAlias": "BAL",
"contractDecimals": 18,
"contractName": "Balancer"
}
},
{
"status": "fulfilled",
"value": {
"methodName": "swapExactTokensForTokens",
"params": {
"amountIn": "100000000000000000",
"amountOutMin": "1451690221859531490",
"deadline": "1800001651169842",
"path": [
"0xba100000625a3754423978a60c9317c58a424e3d",
"0xc02aaa39b223fe8d0a0e5c4f27ead9083c756cc2",
"0x6b175474e89094c44da98b954eedeac495271d0f"
],
"to": "0xd8da6bf26964af9d7eed9e03e53415d37aa96045"
},
"contractAddress": "0xd9e1cE17f2641f24aE83637ab66a2cca9C378B9F"
}
}
]
}
wss://api.blocknative.com/v0ws.send(JSON.stringify({
"timeStamp": new Date().toISOString(),
"dappId": <API KEY>,
"version": "1",
"blockchain": {
"system": "ethereum",
"network": "main"
},
"categoryCode": "simulate",
"eventCode": "txSimulation",
"transaction": {
"from": "0xAb5801a7D398351b8bE11C439e05C5B3259aeC9B",
"to": "0x7a250d5630b4cf539739df2c5dacb4c659f2488d",
"gas": 332160,
"gasPrice": 0,
"input": "0xfb3bdb4100000000000000000000000000000000000000000000003635c9adc5dea000000000000000000000000000000000000000000000000000000000000000000080000000000000000000000000746dff22206ce4e3da6d7eb4d537398be8f236d600000000000000000000000000000000000000000000000000000000624FD77D0000000000000000000000000000000000000000000000000000000000000002000000000000000000000000c02aaa39b223fe8d0a0e5c4f27ead9083c756cc200000000000000000000000094d916873b22c9c1b53695f1c002f78537b9b3b2",
"value": 28981678599856503
}
}))
Name | Type | Description |
|---|---|---|
internalTransactions | [JSON object] | A collection of internal transactions made by the activated contract. Supported calls are decoded. If you wish for your contract to be decoded, contact us on Discord. |
netBalanceChanges | [JSON object] | Contains details of all the balance changes resulting from the internal transactions details in the internalTransactions array. The object is an array with an entry for each address involved in the internal transactions. |
simDetails | JSON object | This object contains details about the simulation, such as blockHeight at the time of calculation, key action timestamps, and end-to-end latency value, in milliseconds. |
contractCall | [JSON object] | This is the top level contract call decoded. If we do not support decoding for this contract, this field will be null. |
gasUsed | Number | Gas used during transaction execution. |
Transaction Preview currently supports Ethereum Mainnet & Goerli Testnet. Please stay tuned for its availability on other networks supported by Blocknative.
Usage rate limit for the Transaction Preview API is 100 requests per 60-second window. Transaction Preview consumes the same daily limits on your Blocknative plan as pending simulated transactions in Simulation Platform. You can view your current consumption on your Blocknative Account Page.
Last modified 6mo ago