Simulating Transactions

Simulating transactions allows you to preview the cost and effect of submitting a transaction without paying fees. You can use this to estimate fees, test a transaction, or to check what the output might be.

To simulate a transaction, you must pass in a transaction and which account would be the signer:

simulate-a-transaction.ts

import {
    Account,
    Aptos,
    AptosConfig,
    Network,
} from "@aptos-labs/ts-sdk";
 
async function example() {
    let sender = Account.generate();
    let receiver = Account.generate();
 
    // 0. Setup the client and test accounts
    const config = new AptosConfig({ network: Network.DEVNET });
    const aptos = new Aptos(config);
 
    await aptos.fundAccount({
        accountAddress: sender.accountAddress,
        amount: 100_000_000,
    }); 
 
    // 1. Build the transaction to preview the impact of it
    const transaction = await aptos.transaction.build.simple({
        sender: sender.accountAddress,
        data: {
        // All transactions on Aptos are implemented via smart contracts.
        function: "0x1::aptos_account::transfer",
        functionArguments: [receiver.accountAddress, 100],
        },
    });
 
    // 2. Simulate to see what would happen if we execute this transaction
    const [userTransactionResponse] = await aptos.transaction.simulate.simple({
        signerPublicKey: sender.publicKey,
        transaction,
    });
    console.log(userTransactionResponse)
 
    // If the fee looks ok, continue to signing!
    // ...
}
 
example();

This will produce the same output as if the transaction was submitted.

Example Output

Terminal

{
  version: '9534925',
  hash: '0xea50b6fbea39ad1ba015d11cda0e7478334669c34830bc3df067a260d680893c',
  state_change_hash: '0x0000000000000000000000000000000000000000000000000000000000000000',
  event_root_hash: '0x0000000000000000000000000000000000000000000000000000000000000000',
  state_checkpoint_hash: null,
  gas_used: '9',
  success: true,
  vm_status: 'Executed successfully',
  accumulator_root_hash: '0x0000000000000000000000000000000000000000000000000000000000000000',
  changes: [
    {
      address: '0x811d5a94ccb597fa2a4f7872a3c678867cff94130d9378c39304c1354ef54abe',
      state_key_hash: '0x09adecee8779b64d05847488e2dbec6679c0c9e2fe618caf0793472ba3a7e4ab',
      data: [Object],
      type: 'write_resource'
    },
    {
      address: '0x811d5a94ccb597fa2a4f7872a3c678867cff94130d9378c39304c1354ef54abe',
      state_key_hash: '0x0c70ede5412277b81d9f8d99369930ed5d56ad65862e3e878ad22dd5500833d0',
      data: [Object],
      type: 'write_resource'
    },
    {
      address: '0xf40c314051890d16ba0a2ba427e003a83e730956fdeccf6c8eebc893a229ddc1',
      state_key_hash: '0x503f9cffb248036da24e18875f3dce72bb33d1d3ef5cfdbdb2fb3411cd718f4f',
      data: [Object],
      type: 'write_resource'
    },
    {
      state_key_hash: '0x6e4b28d40f98a106a65163530924c0dcb40c1349d3aa915d108b4d6cfc1ddb19',
      handle: '0x1b854694ae746cdbd8d44186ca4929b2b337df21d1c74633be19b2710552fdca',
      key: '0x0619dc29a0aac8fa146714058e8dd6d2d0f3bdf5f6331907bf91f3acd81e6935',
      value: '0x708f579f62cb01000100000000000000',
      data: null,
      type: 'write_table_item'
    }
  ],
  sender: '0x811d5a94ccb597fa2a4f7872a3c678867cff94130d9378c39304c1354ef54abe',
  sequence_number: '0',
  max_gas_amount: '200000',
  gas_unit_price: '100',
  expiration_timestamp_secs: '1718983701',
  payload: {
    function: '0x1::aptos_account::transfer',
    type_arguments: [],
    arguments: [
      '0xf40c314051890d16ba0a2ba427e003a83e730956fdeccf6c8eebc893a229ddc1',
      '100'
    ],
    type: 'entry_function_payload'
  },
  signature: {
    public_key: '0x966b6b9aa8feb58ee1b911235dea1f185b9169de56303d18bb59937066881e44',
    signature: '0x00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000',
    type: 'ed25519_signature'
  },
  events: [
    {
      guid: [Object],
      sequence_number: '0',
      type: '0x1::coin::CoinWithdraw',
      data: [Object]
    },
    {
      guid: [Object],
      sequence_number: '0',
      type: '0x1::coin::WithdrawEvent',
      data: [Object]
    },
    {
      guid: [Object],
      sequence_number: '0',
      type: '0x1::coin::CoinDeposit',
      data: [Object]
    },
    {
      guid: [Object],
      sequence_number: '1',
      type: '0x1::coin::DepositEvent',
      data: [Object]
    },
    {
      guid: [Object],
      sequence_number: '0',
      type: '0x1::transaction_fee::FeeStatement',
      data: [Object]
    }
  ],
  timestamp: '1718983681460047'
}

Look here to see the full example of how to build, simulate, and submit a transaction.

You can also learn how to simulate more advanced transactions by looking at the following guides:

Transactions Multi-Agent Transactions