Transaction Simulation

const simulation = await connection.simulateTransaction(
  transaction,
  {
    commitment: 'confirmed',
    sigVerify: false
  }
);

if (simulation.value.err) {
  throw new Error(`Simulation failed: ${simulation.value.err}`);
}

console.log('Compute units used:', simulation.value.unitsConsumed);
console.log('Logs:', simulation.value.logs);

Error: Attempt to debit an account but found no record of a prior credit

Error: Slippage tolerance exceeded

Error: AccountNotFound

Error: Blockhash not found

const simulation = await connection.simulateTransaction(transaction);
const computeUnits = simulation.value.unitsConsumed;

// Add 20% buffer for safety
const computeLimit = Math.ceil(computeUnits * 1.2);

transaction.add(
  ComputeBudgetProgram.setComputeUnitLimit({
    units: computeLimit
  })
);

const simulation = await connection.simulateTransaction(
  transaction,
  { commitment: 'confirmed' }
);

const simulation = await connection.simulateTransaction(
  transaction,
  { sigVerify: false }
);

Program log: Instruction: Swap
Program log: Input: 5000000000 lamports
Program log: Error: Slippage tolerance exceeded
Program log: Expected minimum: 750000000
Program log: Actual output: 745000000