Custom RPC Networks in Phantom: Adding Layer 2s and Private Blockchains Safely

A developer building on Arbitrum or Optimism, or a user managing assets across emerging Layer 2 ecosystems, faces a practical constraint: Phantom Wallet ships with support for a fixed set of mainnet blockchains including Solana, Ethereum, Base, Polygon, Bitcoin, Sui, HyperEVM, and Robinhood Chain. That list covers the largest and most stable networks, but it does not include every chain a user might need to interact with. Custom RPC (Remote Procedure Call) endpoints solve that problem by letting users add new networks directly. The procedure itself is straightforward. The risk, however, lies not in the technical steps but in the endpoints themselves.

When a user adds a custom network to Phantom, they are instructing the wallet to trust a specific server to validate transactions, report account balances, and broadcast signed requests to a blockchain. That trust is not trivial. A malicious or compromised RPC endpoint cannot steal private keys from a self-custodial wallet like Phantom, but it can show false balances, confirm fake transactions, or redirect user funds to a different address than the one displayed. Understanding which endpoints are safe, how to verify them, and when a network is worth adding requires separating marketing claims from technical reality.

Why custom networks matter and what they cost

The built-in networks in Phantom represent a deliberate selection. Solana, Ethereum, and the major Layer 2s have public infrastructure, established communities, and enough transaction volume that Phantom’s parent company can reasonably validate their stability. Adding a custom network does not change Phantom’s non-custodial architecture—the wallet still holds your private keys and signs transactions locally. What it does change is the information source. Instead of connecting to Phantom’s or a major service provider’s vetted node, your wallet begins relying on whatever RPC endpoint you specify.

Layer 2 networks like Arbitrum and Optimism are legitimate examples of why custom RPC support exists. Both are Ethereum-based chains with distinct addresses, token standards, and transaction models. Arbitrum uses a sequencer that batches transactions, while Optimism uses a different rollup mechanism. Neither can be accessed through Phantom’s default Ethereum configuration because their RPC endpoints, transaction formats, and chain identifiers differ. A user holding ARB tokens on Arbitrum, or managing assets on Optimism’s ecosystem, needs a way to connect without switching wallets. Custom networks enable that without requiring Phantom’s developers to pre-integrate every emerging Layer 2.

The cost of adding a network is invisible but real. Every transaction you make on a custom network flows through the endpoint you specified. That endpoint operator can observe your IP address, see your account balance and transaction history, watch which smart contracts you interact with, and understand the timing of your activity. They cannot forge your signature or spend your funds—only you can do that with your private key. But they can deceive you about the current state of the blockchain, and that deception can lead to loss.

Consider a scenario: you receive a message suggesting that a new high-yield farming contract has been deployed on a Layer 2. You add the custom RPC endpoint provided in the message, check your balance in Phantom, approve a transaction to deposit your tokens, and sign. The RPC endpoint shows the transaction as confirmed. But the endpoint operator controlled by a scammer may have never broadcast your transaction to the actual chain. Your tokens remain in your wallet, but you believe they are locked in a contract. Days later, you realize the contract never existed. The RPC endpoint was fake.

Evaluating RPC endpoints and their trustworthiness

The first division is between official, run by the chain and third-party, run by independent operators. Official endpoints are published by the network’s core team or foundation. They may have higher uptime requirements and monitoring, but they also represent a single point of failure. If the official endpoint goes offline, users on that network lose access until it is restored. Third-party RPC providers like Infura, Alchemy, Ankr, and QuickNode offer geographic redundancy and commercial support. However, they introduce a counterparty: a company that can observe all your activity and whose business practices you must evaluate.

For major networks like Arbitrum and Optimism, official documentation lists recommended RPC endpoints. Arbitrum’s portal lists several providers and the official endpoint. Optimism similarly publishes a curated list. Start there. Verify the URL by visiting the official project website directly—do not copy from a forum post, social media, or an email. Phishing via a convincing URL that differs by one character is common. The difference between `rpc.arbitrum.io` and `rpc-arbitrum.io` is one character; one is official, the other may not be.

For new, lesser-known networks or private chains, official endpoints may not exist or may not be public. In those cases, ask which entity operates the endpoint and whether it is a reputable service provider. A private blockchain run by a consortium will often designate which endpoints are safe to use. If you are adding a network to test an application or participate in a small community, the endpoint may be run by the project team themselves. That does not make it trustworthy—it simply clarifies who to hold accountable if something goes wrong.

A second layer of evaluation is uptime and accuracy. Many RPC endpoints publish status pages that show recent outages and average response time. Before adding a network to Phantom for real transactions, test with a small amount. Send a tiny transaction, verify it appears on the chain’s block explorer, and confirm the wallet’s displayed balance matches the explorer’s record. A discrepancy signals that the endpoint may be stale, delayed, or showing fabricated data.

The mechanics of adding a custom network to Phantom

To add a custom network, open Phantom, navigate to Settings, then Networks, then Add Network. You will be asked for several details: the network name (a label for your own reference), the chain ID (a unique identifier for the network), the RPC URL (the endpoint your wallet will connect to), the symbol (the ticker for the native token, like ETH for Ethereum or SOL for Solana), and the block explorer URL (where transactions can be verified). Some fields may be optional depending on Phantom’s version, but the RPC URL is essential.

The chain ID is critical and non-negotiable. Arbitrum One uses chain ID 42161, not 42162. Optimism Mainnet uses 10. Using the wrong chain ID means your transactions will be constructed for a different network than the one you intended, which may cause them to fail or, in rare cases, to succeed on an unintended chain. Always verify the chain ID from the official documentation, not from a user in a Discord channel.

The RPC URL should be a full, valid HTTPS endpoint. It will look like `https://rpc.arbitrum.io/` or `https://endpoints.omniatech.io/v1/optimism/mainnet/public`. Some providers require an API key; you will append it to the base URL. Be aware that sharing your RPC URL with an API key visible to others could allow someone to exhaust your quota or monitor your activity through your account. If you are using a paid endpoint with a personalized key, keep it private to Phantom. Do not post it publicly.

The block explorer URL is useful for verification. After you submit a transaction, Phantom can provide a clickable link to view the transaction on the chain’s public explorer. This lets you independently confirm that your transaction was actually broadcast and settled. For major networks like Arbitrum, the explorer is Arbiscan (arbiscan.io). For Optimism, it is Etherscan (etherscan.io) with a specific subdomain for Optimism. For private or experimental chains, an explorer may not be available, which makes independent verification harder.

Recognizing and avoiding compromised or fake networks

The highest-risk scenarios involve adding a network with the intention of participating in something profitable. A user reads a post claiming that a Layer 2 is launching, offering early access or rewards to participants. The post includes a link to a custom network that can be added to Phantom with one click. The user adds it, sees their balance displayed in Phantom, approves a transaction, and receives a confirmation message. Weeks later, they discover that the network never existed and the RPC endpoint was running a script that simulated the experience.

How to recognize this attack: First, the offer is usually time-limited and exclusive—act now or miss out. Second, the RPC endpoint is provided in the promotional material itself, not sourced independently from official documentation. Third, the network is not listed anywhere on Phantom’s official site, major news outlets, or established Layer 2 aggregators. Fourth, the rewards promise is unrealistic compared to legitimate yield farming or liquidity pools. Fifth, verification is discouraged—you are told to trust the link, not to cross-check it.

Protection requires discipline. If you encounter a network you want to use, pause before adding it. Visit the project’s official website directly via a search engine or a known link, not via a messenger app, forum, or email. Look for an official RPC endpoint listed there. Check whether the project is discussed in established crypto media. Search for recent transaction history on an explorer—if the network is real, there should be transactions you can examine. Verify the chain ID matches multiple sources. Only then add it to Phantom.

A secondary risk involves legitimate networks whose RPC endpoints have been compromised or are experiencing degradation. If you add a correct RPC URL but the endpoint is under attack, poisoned, or overloaded, your wallet may receive inaccurate information. The solution is to have multiple RPC endpoints available and to use an explorer to verify transactions independently. Phantom does not yet support multiple RPC endpoints per network natively, but if you suspect an endpoint is unreliable, you can remove the network and re-add it with a different endpoint.

Managing multiple networks and keeping track of assets

Once you have added several custom networks, Phantom becomes a multi-chain asset manager. You may hold ETH on Ethereum, ARB on Arbitrum, OP on Optimism, and SOL on Solana—all from the same Phantom wallet. The convenience is real, but it creates confusion if you are not careful. Each network uses a separate address, derived from your single Secret Recovery Phrase. This is a feature of the BIP44 standard that most wallets follow: one seed phrase can generate addresses on many chains, each isolated and distinct.

The risk is sending tokens to the wrong network. If you copy what you think is an Arbitrum address from an exchange or application, but it is actually an Ethereum address, and you send Arbitrum tokens to it from Phantom, those tokens are likely lost. Phantom will not prevent you from doing this because both are valid Ethereum-style addresses. The transaction will succeed, but your funds will have moved to an address on the wrong chain that you may not control.

Best practice is to verify the network before sending. In Phantom, double-check that you are on the correct network in the wallet interface. When copying an address, confirm the network it is on. If an exchange or smart contract has provided the address, note what chain it belongs to. Send a small test amount first. Watch it appear on the block explorer to confirm the destination. Only then move larger amounts.

Keeping an asset inventory helps. As you add networks and accumulate balances, track what you hold where. A simple spreadsheet with columns for Asset, Network, Amount, and Address can prevent mistakes. If you ever lose your device or need to recover your wallet, your recovery phrase will regenerate all your addresses, but you will need to remember which networks you used. The addresses themselves will be deterministic—the same seed phrase always generates the same address on the same chain—but you will need to add the custom networks again to Phantom to see your balances.

Security of custom networks in a self-custodial context

Phantom’s self-custodial design means your private keys never leave your device. A compromised RPC endpoint cannot steal them. However, the endpoint can participate in a sophisticated attack. If you are about to approve a token swap or approve a contract to spend your tokens, a malicious RPC endpoint can show you a fake approval screen with different terms. You sign what you believe is a safe transaction, but the endpoint broadcasts something different to the actual network. Your tokens could be transferred to an attacker’s address instead of being swapped.

This attack is hard to execute at scale, but it is possible. The defense is to use transaction preview features wherever available and to verify your activity on a public block explorer immediately after signing. Phantom’s transaction preview shows you what the contract call will do before you sign. Read it carefully. If it says “Transfer 1000 USDC to 0x1234…” and you intended to swap, that is a red flag. Do not sign. Additionally, verify the transaction on the block explorer after it settles. If the actual transaction that appeared on chain is different from what you signed, your endpoint has behaved maliciously and you should not use it again.

The Secret Recovery Phrase remains the highest-value target. Custom networks do not change how to protect it. Write it down, store it offline, and never type it into a website or application. If you are importing your Phantom wallet into another application that asks for your recovery phrase, pause. Legitimate wallets ask for your phrase during import, but phishing attacks also use this approach. Always verify that you are using the official Phantom browser extension downloaded from phantom.com, not from a third-party source or altered version.

Practical workflow for adding Arbitrum or Optimism

Suppose you want to manage assets on Arbitrum. Start by visiting arbitrum.io and locating the RPC information page. The official endpoint is listed there. Open Phantom, go to Settings, Networks, Add Network. Enter: Network Name: “Arbitrum One”, Chain ID: “42161”, RPC URL: “https://rpc.arbitrum.io/”, Native Currency Symbol: “ETH”, Block Explorer: “https://arbiscan.io/”. Verify each field matches the official documentation. Click Add.

Phantom will now show Arbitrum One as an available network. Switch to it and check your address. Copy it carefully. Visit the Arbitrum bridge (bridge.arbitrum.io), connect Phantom, and bridge a small amount of ETH from Ethereum to Arbitrum as a test. Once the bridge transaction settles on both chains, check that your Phantom balance on Arbitrum reflects the arrival. Visit arbiscan.io, search for your address, and confirm the transaction history. If everything matches, you are connected correctly and can add more funds.

For Optimism, the process is identical: visit optimism.io, note the RPC endpoint, add it to Phantom with Chain ID “10”, native currency “ETH”, and block explorer “https://optimistic.etherscan.io/”. Test with a bridge transaction or a small transfer. Verify on the explorer. Only when you have confirmed the connection should you move significant amounts.

When to avoid custom networks and when to use them wisely

Custom networks are genuinely useful for Layer 2s and established sidechains where you have identified a legitimate need. Arbitrum, Optimism, and Base are mature ecosystems with significant liquidity and developer activity. If you are using DeFi applications, trading, or holding assets on these networks, adding them to Phantom is practical and rational. The same applies to testnets if you are developing smart contracts.

Be cautious about experimental networks, private blockchains, or networks promoted primarily via social media. The more nascent the network and the more the opportunity sounds too good to be true, the higher the risk that the RPC endpoint is part of the scam. Test every claim by checking official sources, looking for independent verification, and starting with tiny amounts.

Phantom’s base functionality with pre-integrated networks—Solana, Ethereum, Base, Polygon, Bitcoin, Sui, HyperEVM, and Robinhood Chain—covers the majority of use cases for most users. Custom networks are a power tool, not a necessity for everyone. If you do add them, treat each one as a temporary or deliberate choice, not a permanent convenience. Remove networks you no longer use. Monitor which endpoints you are trusting. Remember that your responsibility as a self-custodial user includes verifying the services you connect to, not just protecting your keys.