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

# HWR Types

Hyperlane Warp Routes (HWR) are Hyperlane's implementation of token bridging, allowing for permissionless transfer of native, ERC20, and synthetic (newly deployed ERC20) assets across any chain via Hyperlane. This document provides details on all HWR types.

| **HWR Types**             | **Description**                                                                                  |
| ------------------------- | ------------------------------------------------------------------------------------------------ |
| Native Token HWR          | Enables direct transfers of native gas tokens (e.g., ETH) across chains without wrapping.        |
| Collateral-Backed ERC20   | Locks ERC20 tokens as collateral on the source chain for cross-chain transfers.                  |
| Synthetic ERC20           | Mints new ERC20 tokens on the destination chain to represent the original tokens.                |
| Hyperlane Warp Routes 2.0 | Allows liquidity to be sourced from multiple collateral tokens.                                  |
| Specialized HWR           | Adds advanced features or integrates with specific use cases (e.g., vaults, fiat-backed tokens.) |

*Please note that this document does not include ERC721 HWR.*

## Core HWR Types

### Native Token HWR

Implemented in `HypNative.sol`, native HWRs handle the transfer of native gas tokens (e.g. ETH on Ethereum or Arbitrum, MNT on Mantle) across different chains.

#### Features

* Directly transfers native tokens without wrapping.
* Uses `msg.value` for transfer amount.
* Handles excess `msg.value` as hook payment.
* Supports donations through a `receive()` function.

See [the implementation](https://github.com/hyperlane-xyz/hyperlane-monorepo/blob/main/solidity/contracts/token/HypNative.sol) for more details.

### Collateral-Backed ERC20 HWR

Implemented in `HypERC20Collateral.sol`, collateral HWRs enable ERC20 tokens to be locked as collateral on the source chain and then used to mint a synthetic representation on the destination chain.

#### Features

* Wraps existing ERC20 tokens as collateral for transfers.
* Locks tokens in the contract on the source chain.
* Releases equivalent tokens on the destination chain.
* Uses SafeERC20 for secure token transfers.

See [the implementation](https://github.com/hyperlane-xyz/hyperlane-monorepo/blob/main/solidity/contracts/token/HypERC20Collateral.sol) for more details.

### Synthetic ERC20 HWRs

Implemented in `HypERC20.sol`, synthetic HWRs mint new tokens on the destination chain that represent the original tokens from the source chain. The original tokens are not transferred but remain locked.

#### Features

* Maintains consistent total supply across all chains.
* Supports custom token attributes (name, symbol, decimals).
* Mints new tokens on the destination chain.
* Burns tokens on the source chain when transferred back.

See [the implementation](https://github.com/hyperlane-xyz/hyperlane-monorepo/blob/main/solidity/contracts/token/HypERC20.sol) for more details.

## Advanced Features

### TokenRouter Functionality

All HWR extend the `TokenRouter` contract, which provides the core functionality for HWR token transfers.

#### Features

1. **Message Structure**: Uses [TokenMessage](https://github.com/hyperlane-xyz/hyperlane-monorepo/blob/main/solidity/contracts/token/libs/TokenMessage.sol) library for encoding and decoding token transfer messages.
2. **Transfer Initiation**: `transferRemote` function initiates cross-chain transfers.
3. **Message Handling**: `_handle` function processes incoming transfer messages.
4. **Abstract Methods**:
   * `_transferFromSender`: Implemented by all HWRs to handle token collection.
   * `_transferTo`: Implemented by all HWRs to handle token distribution.

#### TokenMessage Format

```solidity theme={null}
[32 bytes for recipient][32 bytes for amount][remaining bytes for metadata]
```

This standardized format ensures consistent handling across different HWR implementations while allowing for extensibility through metadata.

See [the implementation](https://github.com/hyperlane-xyz/hyperlane-monorepo/blob/main/solidity/contracts/token/libs/TokenRouter.sol) for more details.

### FastTokenRouter Transfers

Implemented in `FastTokenRouter.sol`, this router extends TokenRouter and provides faster token transfers through a liquidity provider mechanism.

#### Features

* Allows liquidity providers to fulfill transfer requests before message processing.
* Includes a `fastFee` to incentivize liquidity providers.
* Introduces `fastTransferId` for unique transfer identification.

See [the implementation](https://github.com/hyperlane-xyz/hyperlane-monorepo/blob/main/solidity/contracts/token/libs/FastTokenRouter.sol) for more details.

## Specialized HWR Extensions

### 1. Fast Collateral Transfers (FastHypERC20Collateral)

* Combines fast transfer capabilities with collateral-backed ERC20 functionality.
* See [the implementation](https://github.com/hyperlane-xyz/hyperlane-monorepo/blob/main/solidity/contracts/token/extensions/FastHypERC20Collateral.sol) for more details.

### 2. Vault Integration (HypERC4626OwnerCollateral, HypERC4626Collateral)

* Allows for yield generation on collateral by integrating with ERC-4626 vaults.
* See [the implementation](https://github.com/hyperlane-xyz/hyperlane-monorepo/blob/main/solidity/contracts/token/extensions/HypERC4626OwnerCollateral.sol) & [rebasing variant](https://github.com/hyperlane-xyz/hyperlane-monorepo/blob/main/solidity/contracts/token/extensions/HypERC4626Collateral.sol) and for more details.

### 3. Fiat-Backed Tokens (HypFiatToken)

* Designed for stablecoins and other fiat-backed tokens, implementing specific mint and burn operations.
* See [the implementation](https://github.com/hyperlane-xyz/hyperlane-monorepo/blob/main/solidity/contracts/token/extensions/HypFiatToken.sol) for more details.

### 4. Scaled Native Tokens (HypNativeScaled)

* Scales native token values for consistency across chains with different decimals.
* See [the implementation](https://github.com/hyperlane-xyz/hyperlane-monorepo/blob/main/solidity/contracts/token/extensions/HypNativeScaled.sol) for more details.

### 5. xERC20 Integration (HypXERC20 & HypXERC20Lockbox)

* Enables cross-chain transfers of xERC20 tokens, integrating with lockbox mechanisms for conversions.
* See the [HypXERC20 implementation](https://github.com/hyperlane-xyz/hyperlane-monorepo/blob/main/solidity/contracts/token/extensions/HypXERC20.sol) and the [HypXERC20Lockbox implementation](https://github.com/hyperlane-xyz/hyperlane-monorepo/blob/main/solidity/contracts/token/extensions/HypXERC20Lockbox.sol) for more details.

## References

For setup examples & use cases, check out [HWRs: Example Usage](./example-usage).