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

# RebalanceEngine

> Stateless trade executor for vault rebalancing

# RebalanceEngine

The `RebalanceEngine` is a stateless contract that calculates and executes the trades needed to rebalance a vault's portfolio.

## How It Works

When a vault triggers rebalancing:

1. **Calculate**: The engine compares current token weights against target weights
2. **Plan**: It generates a set of `TradeOrder` structs — sells for over-weight tokens, buys for under-weight tokens
3. **Execute**: Trades are executed through the `TokenRouter` with slippage protection

## Trade Execution

```solidity theme={null}
struct TradeOrder {
    address tokenIn;
    address tokenOut;
    uint256 amountIn;
    uint256 minAmountOut;
}
```

* `tokenIn` / `tokenOut`: the swap pair
* `amountIn`: exact amount to sell
* `minAmountOut`: slippage protection (minimum acceptable output)

All trades route through tiltUSDC as the base asset:

* **Sell**: overWeight token → tiltUSDC
* **Buy**: tiltUSDC → underWeight token

## Authorization

Only registered vaults can call `executeRebalance()`. The factory automatically authorizes new vaults on the engine during deployment.

The vault owner or `RebalanceEngine` can also set authorized callers for triggering rebalances externally (e.g., Chainlink Keepers).

## Slippage Protection

Every trade includes a `minAmountOut` parameter calculated from the oracle price minus the configured slippage tolerance. If the execution price is worse than this minimum, the trade reverts.