What is a Harvest Function?

A harvest function is a smart contract method that claims accumulated rewards from DeFi protocols and processes them. Typically by selling reward tokens and reinvesting the proceeds. It's the core mechanism enabling auto-compounding in yield aggregator vaults.

How Harvest Works

Trigger: Keeper bot or user calls harvest()
Claim: Function claims pending rewards
Swap: Reward tokens swapped for deposit asset
Reinvest: Proceeds deposited back into strategy
Accounting: Vault shares updated to reflect gains

Harvest Function Components

```solidity

function harvest() external {

// 1. Claim rewards from farming contract

farmingPool.getReward();

// 2. Swap rewards to want token

uint256 rewardBalance = rewardToken.balanceOf(address(this));

router.swap(rewardToken, wantToken, rewardBalance);

// 3. Reinvest into strategy

deposit(wantToken.balanceOf(address(this)));

}

```

Harvest Timing

Manual Harvest

Anyone can call the function
Often incentivized with small rewards
May be suboptimal timing

Automated Harvest

Keeper bots monitor and execute
Optimized for gas vs reward balance
Services like Gelato, Chainlink Keepers

Harvest Economics

Profitable harvest when:

Reward Value > Gas Cost + Slippage + Caller Incentive

Larger TVL vaults can harvest more frequently because fixed gas costs are spread across more capital.

Caller Incentives

Gas reimbursement
Bounty (% of harvest)
Protocol token rewards
Priority access to harvest

Security Considerations

MEV protection for swaps
Slippage limits
Price oracle checks
Access control on sensitive functions

Harvest in Practice

Beefy Finance harvests range from every few minutes (high TVL) to daily (smaller vaults), optimizing the gas cost vs compounding benefit trade-off.

Harvest Function