MetaMask Custom Network Configuration: Adding Arbitrum, Optimism, and Polygon Without Official Support

A user installing MetaMask extension for the first time may notice that only Ethereum mainnet and a handful of test networks appear in the default dropdown. Major EVM-compatible chains such as Arbitrum, Optimism, and Polygon—networks with billions in total value locked and thousands of active applications—require manual configuration. This is not a limitation of MetaMask itself, but rather a deliberate design choice: the wallet ships with a minimal set of networks to keep the interface clean and reduce initial complexity. When a user needs to interact with decentralized applications on other chains, they must add those networks explicitly.

The process of adding a custom network in MetaMask is straightforward for users who understand what information is required and where to find it. However, the task becomes error-prone without clear guidance on RPC endpoint selection, chain ID validation, and verification that the configuration actually works. Many users either make mistakes that prevent transactions from settling, or worse, accidentally add networks with compromised or slow RPC endpoints that expose their behavior to unreliable intermediaries. Understanding the mechanics of custom network addition is therefore essential for anyone serious about multichain interaction.

Understanding why networks must be added manually

MetaMask is built on a model of decentralized network discovery and user choice rather than a curated list managed by the wallet provider. While Ethereum mainnet and the Sepolia test network are pre-loaded, other networks—even widely used ones like Polygon or Arbitrum—must be added by the user or discovered through a DApp that requests network access. This design avoids having MetaMask encode opinions about which networks are «legitimate» and reduces the maintenance burden of updating the wallet every time a new EVM chain launches.

The practical consequence is that users bear responsibility for verifying network parameters before adding them. Each EVM-compatible blockchain has specific requirements: a unique chain ID, a network name, a currency symbol, and one or more RPC endpoints. These parameters must match the actual network, not a typo or a malicious copy. A user who enters an incorrect chain ID or connects to a fake RPC endpoint may send transactions that appear to succeed but never settle on the correct network, or worse, that settle on an entirely different chain using the same software but a different consensus mechanism.

This is why downloading MetaMask from an official source and verifying the application’s identity before use is a prerequisite for safe multichain operation. Once the wallet is installed and legitimate, adding networks becomes a matter of obtaining correct parameters and entering them carefully. The wallet itself cannot prevent user error—entering a malicious RPC address in a custom network field will still connect to that address—but it can be designed to warn users and offer easy verification steps.

How to locate and validate RPC endpoints

An RPC endpoint is a network node that accepts JSON-RPC requests and returns blockchain data in response. When MetaMask submits a transaction or queries an account balance, it sends that request to one of the RPC endpoints configured for that network. Choosing the right endpoint is therefore more important than it first appears. A slow endpoint delays transaction confirmation and can create confusion about whether a transaction was submitted. A malicious endpoint can see all transactions sent through it, including amounts and destination addresses.

The most reliable approach is to use a public node service that has built a reputation through extended operation. For Arbitrum, Optimism, and Polygon, the official project websites list recommended public RPC endpoints. Arbitrum’s documentation points to Arbitrum’s own RPC or providers such as Infura and Alchemy. Optimism directs users to similar options. Polygon maintains a list that includes endpoints from various providers. These are not the only valid endpoints, but they are tested and widely used.

A secondary approach is to run a personal node. For Polygon, this means running a validator or archive node using the Polygon client software. For Arbitrum and Optimism, it means running a node based on their respective client implementations. Running a node gives absolute control over the endpoint and removes the need to trust a third party, but it requires storage capacity, bandwidth, and the technical knowledge to maintain the software. For most users, selecting from a public provider list is the practical starting point.

After identifying a candidate endpoint, validation involves testing it from within MetaMask. Adding a network with a tentative RPC endpoint and then attempting a simple transaction—such as viewing the native token balance—will reveal whether the endpoint responds. If MetaMask displays an error, the endpoint is either down, misconfigured, or unreachable from the user’s network. Switching to a different endpoint from the same provider or trying a different provider entirely is the appropriate next step. Do not proceed with high-value transactions until at least one transaction has succeeded on the newly added network.

Step-by-step network addition for Arbitrum One

Arbitrum One is the primary scaling solution for Ethereum, processing transactions faster and at lower cost while settling to Ethereum. To add it to MetaMask, access the settings menu by clicking the account icon in the upper right corner of the extension, then selecting «Settings.» From the Settings menu, navigate to «Networks.» At the bottom of the networks list, a button labeled «Add a network» or «Add network» will appear. Click it to open the custom network form.

The form requests: Network Name, New RPC URL, Chain ID, Currency Symbol, and Block Explorer URL. For Arbitrum One, enter «Arbitrum One» as the name, the Arbitrum RPC endpoint as the URL, 42161 as the chain ID, ETH as the currency symbol, and https://arbiscan.io as the block explorer. These values are standardized and publicly documented. Double-checking each field against the official Arbitrum documentation before submitting prevents mistakes that could cause transaction failures.

After clicking «Save,» MetaMask will add Arbitrum One to the network dropdown. The next time the user clicks the network selector at the top of the wallet interface, «Arbitrum One» will be available as an option. Switching to this network changes which RPC endpoint MetaMask uses for subsequent requests, so that balance queries, transaction submissions, and token transfers will all occur on the Arbitrum chain rather than Ethereum mainnet.

A test transaction on the newly added network is strongly recommended. Sending a small amount of ETH or a test token to a known address will confirm that the RPC endpoint is working and that the network parameters are correct. If the transaction appears in the MetaMask activity log but never confirms, or if MetaMask displays an error, the chain ID or RPC endpoint may be incorrect. Delete the network, verify the parameters, and add it again with corrected information.

Adding Optimism and Polygon with similar methodology

Optimism, another major Ethereum scaling solution, follows the same addition process. The network name is «Optimism,» the chain ID is 10, the currency symbol is ETH, and a valid RPC endpoint from Optimism’s documentation (such as https://mainnet.optimism.io) should be used. The block explorer is https://explorer.optimism.io. After adding, test the network by querying a balance or sending a small transaction.

Polygon (formerly Matic Network) is a sidechain rather than a rollup, but from MetaMask’s perspective it is another EVM-compatible chain requiring the same configuration process. The network name is «Polygon,» the chain ID is 137, the currency symbol is MATIC, and the RPC endpoint is typically available from Polygon’s documentation or from providers such as Infura. The block explorer is https://polygonscan.com. Again, after adding, confirm that the network is responsive by checking a balance or submitting a test transaction.

The pattern is consistent across all EVM networks: gather the correct parameters, enter them into the custom network form, save, and then test. Users who need to add multiple networks should follow this process for each one rather than rushing through all additions at once. Testing each network individually prevents confusion later if a transaction fails—you will know whether the problem is the network configuration, the RPC endpoint, the counterparty address, or something else.

For users who prefer not to manually enter parameters, many DApps will request network access when a user attempts to interact with them on an unsupported network. MetaMask will display a dialog offering to add the network automatically based on the DApp’s suggested parameters. This is convenient but requires trusting the DApp to provide correct parameters. Comparing the suggested values against official documentation remains the safest approach even when using automatic addition.

Common errors and how to fix them

The most frequent mistake is entering an incorrect chain ID. Arbitrum One uses 42161; Arbitrum Sepolia (the test network) uses 421614. If a user confuses these, MetaMask will successfully add a network with a mismatched chain ID, and transactions may be broadcast to the wrong chain or rejected entirely. The fix is to delete the network from the Settings > Networks menu and add it again with the correct chain ID. Any tokens or transaction history for that incorrectly configured network will not transfer to the corrected version; the user must re-add the network with the right parameters.

A second common issue is a slow or unresponsive RPC endpoint. MetaMask may hang for several seconds when querying a balance or submitting a transaction if the RPC endpoint is overloaded or geographically distant. The solution is to test an alternative RPC from the provider list or switch to a different provider. Some providers offer both free and paid tiers; paid tiers typically offer higher rate limits and faster responses.

A third error occurs when a user enters an RPC URL that is correct but requires authentication. Some RPC providers issue API keys that must be appended to the endpoint URL. For example, an Infura endpoint might be https://arbitrum-mainnet.infura.io/v3/YOUR_API_KEY. If the API key is missing or incorrect, MetaMask requests will fail with authentication errors. Verify the full URL including any API keys before adding the network.

Block explorer URLs are less critical than RPC endpoints because MetaMask does not use the block explorer for transaction functionality. However, including the correct block explorer URL allows users to click on a transaction hash from MetaMask’s activity log and view the transaction details on a public explorer. If the block explorer URL is wrong, the link will lead to a 404 error. This does not prevent transactions from working, but it reduces visibility into settlement status. Correcting the block explorer URL by editing the network settings will resolve this issue.

Hardware wallet connectivity across custom networks

Users who connect a hardware wallet such as a Ledger or Trezor to MetaMask can use those devices to sign transactions on any custom network that has been added to MetaMask. The hardware wallet device remains the actual custodian of private keys, while MetaMask provides the interface. However, hardware wallets have varying levels of support for different EVM networks. Some devices and firmware versions may require explicit approval for a new network before they will sign transactions on it.

When adding a custom network and then attempting to sign a transaction on it with a hardware wallet, the device may display the network name and chain ID for confirmation. Reviewing this information on the hardware device screen is essential because it confirms that the transaction is intended for the correct chain. If the device rejects the transaction or displays an error, check the device firmware version and consult the device manufacturer’s documentation to determine whether the network is supported.

For users prioritizing security, using a hardware wallet with custom networks adds an additional verification step: the device itself must recognize and approve the network and transaction parameters. This reduces the risk of transaction submission to a malicious network even if MetaMask’s configuration is somehow compromised. The tradeoff is slightly slower transaction signing, since the user must approve each transaction on the device rather than merely entering a password in MetaMask.

When to use public vs. private RPC endpoints

Public RPC endpoints are operated by the project itself or by infrastructure providers and are available to any user without registration. They are convenient and require no setup, but they may have rate limits and can be slow during network congestion. They also expose the user’s IP address and transaction details to the RPC provider, which can be a privacy concern for high-value transactions or users who prefer not to leak their activity patterns to third parties.

Private RPC endpoints are typically purchased from providers such as Alchemy, Infura, Quicknode, or Ankr, and come with higher rate limits and better performance. They still expose transactions to the provider, but the provider is contractually bound to not use that data for other purposes. Some providers offer privacy-focused RPC options that further limit data collection.

Running a personal node gives complete control: the user operates their own RPC endpoint on hardware they control, and no third party sees transactions unless they examine the blockchain itself. This is the most private option but requires technical expertise and ongoing maintenance. The node must stay synchronized with the network, which requires adequate storage and bandwidth.

For ordinary users, a public RPC from an established provider strikes a reasonable balance. For high-value activities or users with stronger privacy concerns, investigating a paid private endpoint or operating a node is worthwhile. The choice depends on the user’s risk tolerance, transaction frequency, and technical capability. Regardless of the choice, testing the selected endpoint before committing significant funds prevents costly mistakes.

Verifying network configuration after addition

After adding a custom network, several verification steps confirm that the configuration is correct and functional. First, switch to the newly added network using the network dropdown at the top of the MetaMask interface. The name of the network should appear in the dropdown and be selectable. Second, confirm that your account address displays the correct prefix or format for the network. Most EVM networks use the same Ethereum-style address format (0x…), but this should be verified against the network’s documentation.

Third, check the native token balance. Each EVM network has a native currency: Arbitrum uses ETH, Optimism uses ETH, Polygon uses MATIC. After adding the network, switch to it and confirm that MetaMask displays a balance for the native currency. If you have never sent funds to this network, the balance will be zero, but the presence of a balance field indicates that the RPC endpoint is responding and the network is recognized.

Fourth, examine the block explorer integration. Click on any transaction in MetaMask’s activity log while on the custom network, and confirm that it opens the correct block explorer. If the link opens a blank page or a different explorer, the block explorer URL may be incorrect. You can edit the network settings to correct it, or you can manually verify transactions by navigating to the block explorer directly and searching for the transaction hash.

Fifth, conduct a test transaction if you have access to native currency on that network. Sending a small amount of the native token to a known address and confirming that it arrives demonstrates that the network is fully functional. If the transaction fails, hangs indefinitely, or produces an error, the RPC endpoint or network configuration requires correction. Do not assume that a successful test cancels the need for caution; always verify critical information before moving significant funds.

Integration with DApps and token interactions

Once a custom network is properly configured, DApps designed for that network can be accessed directly from MetaMask. Visiting a decentralized exchange on Arbitrum, for example, will prompt MetaMask to switch to the Arbitrum network if you are currently on a different network. Approving the network switch allows the DApp to submit transactions on that chain. The same pattern applies to DeFi protocols, NFT marketplaces, and other applications that exist on multiple EVM networks.

Adding tokens to MetaMask on a custom network follows the same process as on Ethereum. If you receive a token on Arbitrum or Polygon, you can import it into MetaMask by navigating to the «Import Tokens» option and entering the token contract address. MetaMask will fetch the token details from a block explorer or registry and add it to your token list. This allows you to see balances and manage transfers of non-native tokens on the custom network.

Users who want to verify that a token contract address is legitimate should check the official project website and the block explorer for the network. Pasting a contract address into MetaMask without verification creates a risk of importing a counterfeit token that mimics the real asset but holds no value. Scammers create fake tokens with similar names and symbols regularly; verifying the contract address against official sources prevents this mistake. If you download MetaMask from a verified source and exercise the same caution with token imports, the multichain experience becomes both functional and safer.

Why understanding configuration prevents costly mistakes

The technical mechanics of adding a custom network to MetaMask may seem straightforward, but the consequences of errors can be expensive. A user who enters the wrong chain ID might send tokens to an address on Arbitrum while the network is configured for a test network, resulting in permanently inaccessible funds. A user who adds a fake RPC endpoint might have their transactions monitored by a malicious party. A user who imports a counterfeit token might invest in a worthless asset. Understanding each parameter, validating each endpoint, and testing before committing real value are the practices that prevent these outcomes.

The goal of learning to configure custom networks is not merely to add Arbitrum, Optimism, and Polygon to MetaMask. It is to develop the habits and skills to safely manage multichain operations. Every time you add a new network or interact with a new DApp, the same verification principles apply. As EVM-compatible networks continue to proliferate, the ability to correctly assess network parameters, select reliable RPC endpoints, and test configurations before moving significant funds becomes increasingly valuable. MetaMask provides the tools; the user provides the diligence that makes the difference between safe multichain access and costly errors.