How to Design a Rollup User Onboarding Flow

Rollup onboarding is the process by which a user transitions from a Layer 1 (L1) blockchain, like Ethereum, to your Layer 2 (L2) rollup. The primary technical challenge is moving assets—typically ETH for gas and ERC-20 tokens for application use—onto the new chain. This requires a secure bridge or native deposit mechanism. For developers, the flow begins with integrating a wallet connector (e.g., MetaMask, WalletConnect) and then guiding the user through funding their L2 account. The user's first experience must be seamless to prevent drop-off, as complex bridging is a major adoption barrier.

The core technical step is facilitating the asset transfer. For Optimistic Rollups like Arbitrum or Optimism, this involves calling the depositETH or depositERC20 function on the L1 bridge contract, which triggers a message to the L2. Zero-Knowledge Rollups like zkSync Era or Starknet have their own L1 Mailbox or Bridge contracts for a similar purpose. Your dApp's frontend should abstract this complexity. Use SDKs like the arbitrum-sdk or zksync-web3 to estimate bridging times and costs, and provide clear, real-time status updates (e.g., "Step 1/3: Confirm L1 transaction"). Never leave the user guessing about transaction state.

Once assets arrive, the user needs gas to transact. On most rollups, the native gas token is ETH, but some use a separate token. Your onboarding must account for this. A best practice is to include a small gas fee subsidy or faucet for first-time users, ensuring they can execute their first transaction immediately after bridging. For example, you could airdrop a minimal amount of gas tokens upon a user's first deposit or provide a faucet link. This eliminates the "dead end" scenario where a user has bridged assets but cannot pay the gas to use them.

The user experience must be intuitive. Implement a progressive disclosure design: show only the necessary steps. Start with a simple "Fund Your Wallet" button that detects if the user is on the correct network. If not, prompt a network switch via wallet_addEthereumChain. Then, offer a default bridge option with a pre-calculated minimum recommended deposit. For advanced users, provide a toggle for custom amounts and bridge selection. Always display the estimated wait time—~10 minutes for Optimistic Rollups and ~10-30 minutes for ZK Rollups—managing expectations is key.

Finally, onboard users into your specific application. After funding, automatically redirect them to a tutorial or a first actionable step, like approving a token for a DEX or minting an NFT. Use this moment to educate users about rollup benefits: lower fees and faster transactions. Track onboarding completion rates with analytics to identify friction points, such as high drop-off at the bridge confirmation step. Continuously iterate based on data. A smooth onboarding flow directly correlates with higher user retention and successful protocol growth.

Designing a rollup onboarding flow requires understanding the user's journey from a base layer like Ethereum to your rollup. The primary technical challenge is managing asset bridging and account abstraction. Users need a seamless way to move funds and pay for transactions without holding the rollup's native gas token. A common solution is a paymaster that sponsors initial gas fees, allowing users to transact immediately after bridging. The flow typically involves: a frontend interface, a bridge smart contract, a paymaster service, and integration with the rollup's RPC endpoint.

The first step is implementing a secure bridge for depositing assets. For an EVM-compatible rollup like Optimism or Arbitrum, this involves deploying a bridge contract on L1 that locks tokens and mints corresponding representations on L2. Use the official Canonical Bridge standards where possible for security and interoperability. The frontend must then track the deposit status, which can take 10-20 minutes for L1 finality. To improve UX, consider implementing fast bridges or liquidity networks for instant credit, though these introduce additional trust assumptions and complexity.

Next, integrate account abstraction (ERC-4337) to enable gas sponsorship. Deploy a paymaster contract on the rollup that can validate and pay for user operations (UserOperation). The paymaster logic should verify a user's eligibility—often by checking for a recent deposit from a whitelisted bridge—before sponsoring gas. This allows users to execute their first transaction, like swapping tokens or adding liquidity, without first acquiring ETH on the rollup. Monitor paymaster funds closely, as depletion will halt the onboarding process.

Security is paramount. The bridge and paymaster contracts are high-value targets. Conduct thorough audits and consider timelocks and multi-signature controls for admin functions. For the user-facing application, implement robust transaction simulation to preview outcomes and prevent failed transactions that still incur gas costs. Use wallet connection libraries like WalletConnect or Web3Modal to support a wide range of wallets, ensuring you don't exclude users based on their existing wallet provider.

Finally, test the entire flow extensively on a testnet. Simulate high congestion and monitor gas estimates. Provide clear error messages and status updates at each stage: wallet connection, approval, deposit, L2 confirmation, and initial transaction. A successful flow reduces friction to near-zero, enabling users to interact with your rollup's dApps within minutes of their first visit, which is essential for competing in the current layer-2 landscape.

The primary goal of a rollup onboarding flow is to guide a user from a base layer (like Ethereum mainnet) onto your rollup network. This involves two key technical processes: funding a wallet on the new chain and bridging assets. Architecturally, the flow typically begins with a wallet connection step, where you integrate with providers like MetaMask or WalletConnect to authenticate the user and access their base-layer account. The next component is the gas estimation system, which must calculate fees for both the initial approval (if using an ERC-20) and the bridge deposit transaction, presenting a clear total cost to the user.

A robust flow must handle the asset bridging logic. For native ETH, this is a direct deposit to the rollup's bridge contract. For ERC-20 tokens, it requires a two-step process: a token approval followed by the deposit. Your architecture should abstract this complexity. Services like the Socket API or LI.FI SDK can be integrated to handle multi-chain liquidity and routing, simplifying the backend. The UI must then track this transaction through its lifecycle—from submission on L1 to finalization on L2—providing clear status updates.

Finally, the post-bridge experience is crucial. Once assets arrive, the flow should automatically switch the user's connected network to the rollup (e.g., from Ethereum Mainnet to Arbitrum One) using methods like wallet_addEthereumChain. The architecture should then facilitate the first on-rollup actions, such as displaying available DApps or prompting a simple swap in a built-in DEX aggregator to demonstrate low fees. This closed-loop design ensures the user completes a full cycle, moving from an external asset to an active participant within your rollup's ecosystem.

A well-designed onboarding flow is critical for rollup adoption, as it directly addresses the primary friction point for new users: managing native gas tokens. Unlike the base layer, rollups like Arbitrum, Optimism, and zkSync require users to hold and pay fees in their specific native token (e.g., ETH on Arbitrum). A gas abstraction flow allows a user's first interactions—such as bridging assets or swapping tokens—to be sponsored by the application or a third-party paymaster, eliminating the need for the user to acquire gas tokens upfront. This creates a signup experience comparable to Web2.

The core technical component enabling this is the ERC-4337 Account Abstraction standard, which introduces a UserOperation object and a Paymaster contract. Instead of a traditional transaction, a user's intent is bundled and sponsored. For a rollup onboarding flow, you typically integrate a smart contract wallet (like Safe or a custom SimpleAccount) and a paymaster service. The paymaster can be funded by the dApp to cover initial gas costs or can implement logic to accept payment in any ERC-20 token the user possesses, converting it to the rollup's native gas token via a swap.

A practical onboarding sequence involves several steps. First, the user connects their EOA (e.g., MetaMask) from the base chain. Your dApp then prompts them to deploy a smart contract wallet on the target rollup, signing a UserOperation for this deployment. This initial operation is sponsored by your paymaster. Once the wallet is deployed, the user can execute their first action—like bridging USDC from Ethereum to Arbitrum. The bridging transaction is also sponsored, allowing the user to receive bridged USDC on Arbitrum without ever holding ARB-ETH.

Key design considerations include sponsorship limits to prevent abuse, session keys for temporary gasless permissions, and fallback mechanisms. For example, you might sponsor a user's first five transactions or the first $5 in gas fees. It's also crucial to inform users when sponsored gas is ending and guide them on how to acquire the rollup's native token for self-custodial operations. Transparency about sponsorship builds trust.

To implement this, you would use SDKs from providers like Stackup, Biconomy, or Candide, or interact directly with a bundler and paymaster contract. A basic code snippet for creating a sponsored UserOperation with the userop.js library might look like:

javascriptCopy
const userOp = await client.buildUserOperation({
  sender: smartWalletAddress,
  callData: encodeCallData(
    ['address', 'uint256'],
    [recipient, amount]
  ),
  paymasterAndData: paymasterAddress,
});
const sponsoredUserOp = await client.estimateUserOperationGas(userOp);

This constructs a transaction where the paymaster at paymasterAddress will cover the gas.

Ultimately, a gasless onboarding flow removes a major adoption barrier. By abstracting gas complexities, you enable users to experience your dApp's core value immediately. This strategy is essential for rollup-based applications aiming for mainstream user growth, turning a multi-step, technical process into a single-click experience.

A unified onboarding script consolidates the fragmented steps of moving a user from Ethereum mainnet to a rollup into a single, developer-friendly function. The core challenge is managing multiple asynchronous operations: detecting the user's wallet and network, checking their token balances, initiating a bridge transaction, and optionally sponsoring gas fees on the destination chain. This script acts as a middleware layer, abstracting the complexity of cross-chain interactions for your dApp's frontend. Popular libraries like wagmi and viem provide the essential building blocks for wallet connection and transaction construction.

The script's logic begins with wallet and network validation. Using wagmi, you check if a user's wallet (e.g., MetaMask) is connected to Ethereum Mainnet. If not, you must prompt them to switch networks. Next, you query the user's balance of the required asset (ETH or a specific ERC-20) using the getBalance function from viem. This step is critical for pre-transaction validation to avoid user errors and failed transactions due to insufficient funds.

For the bridge operation, you integrate with a bridge provider's SDK or smart contract interface. For a native ETH bridge, this involves constructing a transaction that calls the L1 bridge contract's depositETH function, with the rollup's gateway address and the user's L2 address as parameters. The script must handle the transaction lifecycle—signing, sending, and waiting for confirmations—while providing clear user feedback. For a smoother experience, consider implementing transaction receipt polling to detect when funds arrive on L2.

A key feature of advanced onboarding is gas abstraction. Instead of requiring users to hold the rollup's native gas token upfront, you can sponsor their first transactions. The script can be designed to estimate the gas required for a user's initial L2 action (like swapping or providing liquidity) and include a gas sponsorship meta-transaction via a paymaster contract. This requires integrating with the rollup's SDK (e.g., Starknet.js, zkSync SDK) to craft and relay a sponsored transaction, dramatically improving the new user experience.

Finally, the script must be robust against failures. Implement comprehensive error handling for each stage: network switch rejections, insufficient balance errors, bridge contract reverts, and RPC timeouts. Wrap core functions in try/catch blocks and provide human-readable error messages. Log key events (e.g., "Bridge transaction sent: 0x...") to the console for debugging. The complete script should export a single asynchronous function, like onboardToRollup(userAddress, amount), that returns a success state and a transaction hash, making it easily callable from any UI component.

Designing a rollup onboarding flow requires balancing user experience with technical constraints. The core principles remain consistent: minimize friction, abstract complexity, and ensure security. Key takeaways include implementing social logins or embedded wallets to bypass seed phrases, using paymaster services for gas sponsorship, and providing clear transaction status updates via a block explorer. Always test flows on testnet with real users to identify pain points before mainnet deployment.

For developers ready to build, start with the Account Abstraction SDKs from providers like Stackup, Biconomy, or ZeroDev. These tools handle the complexity of ERC-4337 smart accounts and paymasters. For bridging, integrate a solution like Socket or Li.Fi for a unified interface. Remember to implement session keys for repeated dApp interactions and consider batched transactions to reduce costs for complex user journeys. Your smart contract architecture must support these modular components.

The next evolution in onboarding is intent-based design. Instead of signing specific transactions, users express a goal (e.g., "swap 1 ETH for USDC"), and a solver network constructs and executes the optimal path. Projects like Anoma and Essential are pioneering this approach. To stay current, monitor EIP-7702 for native AA on Ethereum L1 and follow rollup-specific developments like zkSync's native account abstraction. The goal is to make interacting with a rollup as seamless as using a traditional web application.

Continue your research with these essential resources: the ERC-4337 official documentation, Vitalik's blog post on account abstraction, and the Rollup-as-a-Service (RaaS) guides from platforms like Caldera and Conduit. For community discussion, engage with forums on the Ethereum Magicians website or the r/ethereum subreddit. Building a superior onboarding experience is a continuous process of iteration informed by user feedback and advancing infrastructure.