Although there is only one Ethereum blockchain, usually called “Mainnet”, there are many different Ethereum-compatible networks, serving a variety of purposes.
By default, MetaMask supports connecting to six different networks: Mainnet, four popular test networks (Goerli, Kovan, Rinkeby, Ropsten), and a “Localhost” network used by software developers.
However, MetaMask can connect to any Ethereum-compatible network. We call these networks custom networks, because they are usually customized to solve a particular problem. As of version 9.1.0 of the MetaMask browser extension (the feature is pending for the mobile app), websites can ask you to connect to a particular network in MetaMask, and add its information if it doesn’t exist yet.
The most common use case for custom networks at the time of writing are so-called “Layer-2” or “L2” networks, whose purpose are to “scale” Ethereum. Usually, the operators of these networks will usually ask you to deposit funds or assets on Mainnet in order to use them on the Layer-2 network, which may offer cheaper and faster transactions. Examples of these networks include Optimism, Polygon, SKALE, and xDAI.
Before you use a custom network with MetaMask, it’s important to understand the risks of adding and interacting with custom networks. MetaMask does not verify custom networks. You are responsible for verifying any custom network added to MetaMask. We strongly recommend reading this article to ensure that you don’t put your privacy or funds at risk.
At MetaMask, we believe that custom networks — especially Layer 2 networks — have an important role to play in Ethereum’s future. However, their benefits do not come without risks. Here are some important things to keep in mind when using custom networks:
- Only add custom networks via the custom network request confirmation. It is possible to add custom networks manually via settings, but any legitimate custom network can be added by using the request. There is probably no reason to do it manually unless you are a software developer.
- Always verify custom network information. When a website asks you to add a custom network, how do you know that you can trust the information? We have some recommendations in our verification guide.
- Although a custom network may be Ethereum-compatible, they are not the same as the Ethereum Mainnet. You may have the same Ethereum addresses on all networks, but your assets and transactions are specific to each network, unless the custom network provider allows you to move funds in to and out of it.
- MetaMask cannot track transactions between networks. You are responsible for understanding how any cross-network transactions or deposits work. Make sure you trust the network operator and any Ethereum address you send funds to.
- Not all networks are safe. In order to offer e.g. cheaper and faster transactions, custom networks usually have different security and reliability guarantees than Mainnet. Try to understand the risks before moving significant value to a custom network.
Make sure you trust the network provider. A malicious network provider can lie about the state of the blockchain, withhold transactions, and record your network activity and IP address.