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

# Universal Router

> Unified entry point for executing swaps across V2 and V3 protocols

# Universal Router

The **Universal Router** is a single smart contract that can execute swaps across both V2 and V3 pools. It serves as the unified entry point for all trading operations on Kroko DEX.

## Why a Universal Router?

Without it, swapping through V2 and V3 would require separate contracts and separate transactions. The Universal Router:

* **Unifies execution** — One contract handles V2, V3, and mixed-protocol swaps
* **Enables complex routes** — Multi-hop swaps that cross between V2 and V3 pools
* **Reduces gas** — Batches operations in a single transaction
* **Integrates Permit2** — Pulls tokens via Permit2 for streamlined approvals

## How It Works

The Universal Router receives encoded **commands** and **inputs** via its `execute()` function:

```solidity theme={null}
function execute(
    bytes calldata commands,
    bytes[] calldata inputs,
    uint256 deadline
) external payable;
```

* **commands**: A byte string where each byte is a command code (e.g., V2\_SWAP\_EXACT\_IN, V3\_SWAP\_EXACT\_IN, WRAP\_ETH, UNWRAP\_WETH, etc.)
* **inputs**: ABI-encoded parameters for each command
* **deadline**: Unix timestamp after which the transaction reverts

## Typical Swap Flow

```
1. Swap API finds the optimal route
2. Swap API encodes the route as Universal Router commands
3. Frontend receives { to, data, value } from the API
4. User signs and sends the transaction
5. Universal Router executes the commands sequentially
```

Developers do **not** need to encode commands manually — the Swap API handles this. You simply forward the response:

```typescript theme={null}
const tx = await signer.sendTransaction({
  to: swapData.to,      // Universal Router address
  data: swapData.data,  // Encoded execute() calldata
  value: swapData.value // Native KAS amount (0 for ERC-20 to ERC-20)
});
```

## Slippage Protection

The encoded calldata includes on-chain slippage checks:

| Trade Type   | Protection     | Description                        |
| ------------ | -------------- | ---------------------------------- |
| Exact Input  | `minAmountOut` | Reverts if output is below minimum |
| Exact Output | `maxAmountIn`  | Reverts if input exceeds maximum   |

These checks are enforced by the Universal Router on-chain, not just the API.

## Native KAS Handling

When a swap involves native KAS (not WKAS), the Universal Router automatically:

* **Selling KAS**: Wraps the KAS sent as `msg.value` into WKAS before the swap
* **Buying KAS**: Unwraps WKAS to KAS and sends it to the recipient after the swap

The `value` field in the Swap API response is non-zero when native KAS is the input token.