Using the Standard Bridge

Certain interactions, like transferring ETH and ERC-20 tokens between the two networks, are common enough that we've built the "Standard Bridge" to make moving these assets between L1 and L2 as easy as possible.

The standard bridge functionality provides a method for an ERC-20 token to be deposited and locked on L1 in exchange of the same amount of an equivalent token on L2. This process is known as "bridging a token", e.g. depositing 100 USDC on L1 in exchange for 100 USDC on L2 and also the reverse - withdrawing 100 USDC on L2 in exchange for the same amount on L1. In addition to bridging tokens the standard bridge is also used for ETH.

The Standard Bridge is composed of two main contracts the L1StandardBridge (opens in a new tab) (for Layer 1) and the L2StandardBridge (opens in a new tab) (for Layer 2). The contract addresses can be found here.

Here we'll go over the basics of using this bridge to move ERC-20 assets between Layer 1 and Layer 2.

Deposits

Depositing ERC20s

ERC20 deposits into L2 can be triggered via the depositERC20 and depositERC20To functions on the L1StandardBridge (opens in a new tab). You must approve the Standard Token Bridge to use the amount of tokens that you want to deposit or the deposit will fail.

Note that the bridge does not support certain ERC-20 configurations:

• Fee on transfer tokens (opens in a new tab)
• Tokens that modify balances without emitting a Transfer event (opens in a new tab)

Note that if you use the OP Mainnet bridge UI (opens in a new tab), or the Optimism SDK (opens in a new tab) which automatically chooses the correct bridge contract, so this problem does not happen.

There are two ways to check if a token can use the standard bridge:

1. Look in the token list (opens in a new tab). If a token can use the standard bridge, then the "chainId": 10 entry will have the standard L2 bridge address, 0x4200..0010. For example, this entry shows that on OP Mainnet 0xBTC can use the standard bridge.

       {
      "chainId": 10,
      "address": "0xe0BB0D3DE8c10976511e5030cA403dBf4c25165B",
      "name": "0xBitcoin",
      "symbol": "0xBTC",
      "decimals": 8,
      "logoURI": "https://ethereum-optimism.github.io/data/0xBTC/logo.png",
      "extensions": {
        "optimismBridgeAddress": "0x4200000000000000000000000000000000000010"
      }
    },

   If the token exists in the token list but does not use the standard bridge, the extensions.optimismBridgeAddress value is different. For example, this entry shows that on OP Mainnet DAI uses a different bridge:

       {
      "chainId": 10,
      "address": "0xDA10009cBd5D07dd0CeCc66161FC93D7c9000da1",
      "name": "Dai stable coin",
      "symbol": "DAI",
      "decimals": 18,
      "logoURI": "https://ethereum-optimism.github.io/data/DAI/logo.svg",
      "extensions": {
        "optimismBridgeAddress": "0x467194771dAe2967Aef3ECbEDD3Bf9a310C76C65"
      }
    },

2. You can "ask" the L2 token contract by calling it. ERC-20 tokens that can use the standard bridge not only if they:

   • Have an l2Bridge method
   • That method returns 0x4200...0010.

   For example, this link (opens in a new tab) can be used to see that 0xBTC uses the standard bridge.

   Note that you cannot query the L1 token contract the same way. L2 contracts know the identity of their L1 counterpart, but L1 contracts only need to implement the standard ERC-20 methods.

Depositing ETH

ETH deposits into L2 can be triggered via the depositETH and depositETHTo functions on the L1StandardBridge (opens in a new tab). ETH deposits can alternatively be triggered by sending ETH directly to the L1StandardBridge. Once your deposit is detected and finalized on OP Mainnet, your account will be funded with the corresponding amount of ETH on L2.

Depositing USDC

USDC issued by Circle will be native to OP Mainnet and can be considered the official form of USDC for the ecosystem. Over time, native USDC liquidity may grow and replace the currently circulating bridged USDC liquidity that comes from Ethereum.

Withdrawals

Withdrawing ERC20s

ERC20 withdrawals can be triggered via the withdraw or withdrawTo functions on the L2StandardBridge (opens in a new tab). If you'd like to see this contracts in action, you should check out the L1 ⇔ L2 deposit-and-withdraw example.

Withdrawing ETH

Unlike on L1, we do not have a separate function on L2 for withdrawing ETH. Instead, you can use the withdraw or withdrawTo functions on the L2StandardBridge (opens in a new tab) and use the address 0xDeadDeAddeAddEAddeadDEaDDEAdDeaDDeAD0000 as the L2 token address.

Adding an ERC20 token to the Standard Bridge

The Superchain token list

The Standard bridge allows a one-to-many mapping between L1 and L2 tokens, meaning that there can be many OP Mainnet implementations of an L1 token. However there is always a one-to-one mapping between L1 and L2 tokens in the Superchain token list. The Superchain token list is used as the source of truth for the OP Mainnet bridge UI (opens in a new tab) which is the main portal for moving assets between Layer 1 and Layer 2.

If you want to have your token added to the Superchain token list, you must make a pull request against the Superchain token list repository (opens in a new tab). You'll need the addresses for both the L1 and L2 tokens, as well as a logo for the token. If you're looking for an example to follow, take a look at this simple pull request (opens in a new tab) that adds a token to the token list.