> ## Documentation Index
> Fetch the complete documentation index at: https://docs.berachain.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Flash Loans

> Uncollateralized borrow-and-repay within one transaction; flashLoan flow, callback, and implementation steps.

Flash loans let you **borrow without collateral** as long as you repay in the same transaction.

## Flash loans in Bend

In Bend, flash loans:

* Require no collateral
* Must be repaid in the same transaction
* Execute in one block
* Are aimed at developers and advanced users

## How they work

The Morpho contract exposes `flashLoan` and uses a callback to complete the flow.

### Flow

1. **Initiate**: Your contract calls `morpho.flashLoan(token, amount, data)`.
2. **Receive**: Morpho transfers the requested amount to your contract.
3. **Callback**: Morpho calls `onMorphoFlashLoan(amount, data)` on your contract.
4. **Logic**: Your contract runs its logic (arbitrage, swap, etc.).
5. **Repay**: Your contract approves Morpho to pull back the borrowed amount.
6. **Complete**: Morpho pulls the funds. If repayment fails, the whole transaction reverts.

## Implementation

To use flash loans:

1. Implement a contract that conforms to `IMorphoFlashLoanCallback`.
2. Implement `onMorphoFlashLoan` with your logic.
3. In the callback, approve the Bend (Morpho) contract to pull the borrowed amount before returning.

## Use cases

* **Arbitrage**: Profit from price differences across protocols in one transaction
* **Collateral swap**: Replace one collateral type with another in one transaction
* **Self-liquidation**: Liquidate your own position to avoid third-party liquidation
* **Flash actions**: Combine several Bend operations in one transaction

## Security

* **Atomicity**: If the callback doesn't approve repayment, the transaction reverts.
* **Funds**: Don't leave funds in the flash loan contract after the callback.
* **Reentrancy**: Be careful calling external contracts inside the callback.
* **Gas**: Flash loan flows can use a lot of gas.

## Bend callbacks

Bend supports additional callbacks for richer flows:

* `IMorphoLiquidateCallback`: Liquidations
* `IMorphoRepayCallback`: Repayments
* `IMorphoSupplyCallback`: Supply
* `IMorphoSupplyCollateralCallback`: Supply collateral

You can combine supply, borrow, repay, and withdraw in a single transaction using these callbacks.