How to Design a Gasless Transaction Onboarding Flow

Gasless onboarding allows users to interact with a dApp without holding the native blockchain token (like ETH) to pay for transaction fees, or gas. This is achieved by having a third party, typically the dApp developer or a dedicated relayer, sponsor these costs. The core mechanism enabling this is EIP-4337: Account Abstraction, which separates transaction execution from fee payment. Instead of a standard Externally Owned Account (EOA), users interact with a smart contract wallet. This contract can validate a user's signature and then have its gas paid by another account, creating a seamless, fee-free entry point.

Designing the flow starts with choosing an implementation path. For Ethereum and EVM chains, the dominant standard is ERC-4337 UserOperations bundled by a Bundler and sponsored via a Paymaster. Alternatively, you can use existing SDKs from providers like Biconomy, Stackup, or Candide. The key components are: a smart contract wallet (e.g., a minimal SimpleAccount), a paymaster contract that holds gas funds and defines sponsorship rules, and a relayer network to submit transactions. The user experience should abstract all this complexity, presenting only a familiar social login or email sign-up.

A basic implementation involves setting up a paymaster. Below is a simplified example of a verifying paymaster contract in Solidity that sponsors gas for a specific dApp. It uses the UserOperation struct defined by ERC-4337.

solidityCopy
// SPDX-License-Identifier: GPL-3.0
import "@account-abstraction/contracts/interfaces/IEntryPoint.sol";
import "@account-abstraction/contracts/interfaces/UserOperation.sol";

contract VerifyingPaymaster {
    IEntryPoint public immutable entryPoint;
    address public immutable allowedSponsor;

    constructor(IEntryPoint _entryPoint, address _sponsor) {
        entryPoint = _entryPoint;
        allowedSponsor = _sponsor;
    }

    function validatePaymasterUserOp(
        UserOperation calldata userOp,
        bytes32 userOpHash,
        uint256 maxCost
    ) external returns (bytes memory context, uint256 validationData) {
        // Add logic to verify sponsorship (e.g., whitelisted dApp address)
        require(userOp.sender == allowedSponsor, "Paymaster: Sender not allowed");
        // Return zero validationData for success
        return ("", 0);
    }
}

The entryPoint is the system's singleton contract, and the allowedSponsor could be your dApp's contract address.

For the frontend, integrate an SDK like @biconomy/account to create a gasless transaction. The code hides the UserOperation construction and relay logic. Here's a pattern using Biconomy:

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import { BiconomySmartAccount } from "@biconomy/account";
import { ethers } from "ethers";

// 1. Initialize provider and signer (e.g., from social login)
const provider = new ethers.providers.Web3Provider(window.ethereum);
const signer = provider.getSigner();

// 2. Create Biconomy Smart Account instance with paymaster
const smartAccount = new BiconomySmartAccount({
    signer: signer,
    chainId: ChainId.POLYGON_MUMBAI,
    paymasterApiKey: process.env.BICONOMY_PAYMASTER_KEY // Enables gas sponsorship
});
await smartAccount.init();

// 3. Build a gasless transaction
const transaction = {
    to: recipientAddress,
    data: "0x", // Or encoded contract call
    value: ethers.utils.parseEther("0.1")
};

// 4. Send the transaction - user signs, but pays no gas
const userOpResponse = await smartAccount.sendTransaction(transaction);
const txHash = await userOpResponse.wait();

The user signs a message, which is packaged into a UserOperation. The Biconomy infrastructure bundles it and uses your configured paymaster to cover the gas fees on Polygon.

Critical design considerations include managing sponsor costs and security. You must fund the paymaster contract with ETH or the chain's native token, and monitor its balance. Implement rate-limiting or whitelists to prevent abuse. Security is paramount: the paymaster's validation logic must be robust to avoid sponsoring malicious transactions. Furthermore, always inform users about the sponsorship model and what happens when it ends. A best practice is to gradually transition users to self-custody, perhaps by gifting them a small amount of native gas token after initial interactions, as done by protocols like Coinbase Wallet's onboarding.

The impact of a well-designed gasless flow is significant. It reduces user drop-off by an estimated 50-70% for first-time Web3 interactions. By removing the need to acquire crypto from an exchange upfront, you unlock mainstream adoption. The future is session keys enabled by account abstraction, allowing users to approve a series of transactions (e.g., in a game) with one gasless sign-in. Start by prototyping on a testnet with a service provider, measure the onboarding conversion metrics, and iterate based on real user behavior before deploying a production system on mainnet.

A gasless transaction flow allows users to interact with a dApp without needing to hold the native blockchain token (e.g., ETH for Ethereum) to pay for transaction fees (gas). This is essential for onboarding users unfamiliar with crypto mechanics. The core architectural pattern involves a relayer or paymaster that sponsors the gas costs on behalf of the user. You must understand the two primary models: meta-transactions (ERC-2771 with a trusted forwarder) and account abstraction (ERC-4337 with paymasters). Your choice depends on whether you're modifying existing smart contracts or building new ones with user-friendly smart accounts.

Before writing any code, you need to set up your development environment and choose supporting infrastructure. For a meta-transaction approach, you'll need a relayer service. Options include running your own using the OpenZeppelin Defender Relayer, or using a managed service like Biconomy or Gelato. For ERC-4337, you need a bundler and a paymaster. You can start with the official Stackup Bundler and a testnet paymaster. Install necessary libraries: for ethers.js or viem, and specific SDKs like @biconomy/account or @account-abstraction/sdk.

Your smart contracts must be designed to support your chosen gasless method. For meta-transactions, your contract must inherit from ERC2771Context (OpenZeppelin) and trust a Forwarder contract address. This verifies the relayed call's signature. For ERC-4337, you will deploy a smart account factory and a paymaster contract. The paymaster can implement sponsorship logic, such as whitelisting your dApp's operations or using ERC-20 tokens for fees. Test all contracts extensively on a testnet like Sepolia or Goerli, using tools like Hardhat or Foundry, before considering mainnet deployment.

On the client side, you must integrate an SDK to craft user operations. For ERC-4337, this involves creating a UserOperation object, having it signed by the user's key, and sending it to a bundler. The user signs a message, not a transaction, which is a fundamentally different UX. Handle edge cases: what happens if the paymaster's deposit runs out, or if the relayer is offline? Implement clear user feedback for these states. Always include a fallback; allow users to pay gas themselves if the sponsored flow fails, ensuring your application remains functional.

Security is paramount. For meta-transactions, ensure your forwarder contract is secure and non-upgradable to prevent malicious relayer takeovers. For paymasters, implement strict validation rules to prevent draining of funds. Use rate limiting and require signatures for privileged actions. Thoroughly audit any third-party relayer or bundler service you integrate. Finally, calculate the economic model. Sponsoring gas is a cost to your project. Estimate average transaction costs and budget accordingly, potentially exploring models where fees are paid in your dApp's ERC-20 token via the paymaster to offset costs.

A gasless onboarding flow allows new users to interact with a dApp without needing to purchase native tokens for transaction fees. This is achieved using a paymaster, a smart contract that can sponsor a user's gas costs. The core design pattern involves the dApp backend or a designated sponsor paying for gas in a stable token like USDC, or even off-chain, while the user signs a meta-transaction. Popular solutions include ERC-4337 Account Abstraction's native paymaster system, Gelato Network's Relay, and OpenZeppelin Defender. The primary goal is to remove the initial friction of acquiring ETH or MATIC, which is a significant barrier to mainstream adoption.

Designing the flow starts with defining the sponsorship model. Common approaches include: a dApp-pays model where the project covers costs for acquisition, a fee-on-transfer model where gas is deducted from the transaction value in a stablecoin, or a subscription model. You must integrate a paymaster contract that validates sponsorship logic, such as checking a whitelist or verifying a signed message from a backend server. For ERC-4337, the UserOperation includes a paymasterAndData field that routes the transaction to your custom paymaster contract for validation and payment.

Here is a simplified conceptual flow for an ERC-4337 paymaster:

solidityCopy
// Example validation logic in a paymaster contract
function validatePaymasterUserOp(
    UserOperation calldata userOp,
    bytes32,
    uint256
) external view returns (bytes memory context, uint256 validationData) {
    // 1. Verify the dApp backend authorized this user/sponsorship
    require(_isValidSignature(userOp), "Invalid sponsor signature");
    // 2. Optional: Check a whitelist or rate limit
    require(whitelist[userOp.sender], "Sender not whitelisted");
    // 3. If validation passes, paymaster agrees to pay
    return ("", 0);
}

After validation, the paymaster's postOp function handles reimbursement from its deposited funds.

On the client side, you need a library that supports gasless transactions. For ERC-4337, use the account-abstraction SDK or UserOperation bundlers like those from Stackup or Alchemy. The user signs a message (the UserOperation), which is sent to a bundler. The bundler packages it and the designated paymaster contract pays the gas. Critical considerations include setting appropriate sponsorship limits to prevent abuse, implementing robust signature verification to ensure only intended transactions are sponsored, and monitoring paymaster deposit balances to avoid service interruption.

Best practices for a production flow involve gradual decentralization. Start with a whitelisted, dApp-funded paymaster for onboarding, then offer users a seamless transition to a hybrid model where they can opt into paying fees themselves after initial engagement. Always provide clear UX indicators showing when a transaction is sponsored. Security is paramount: audit your paymaster contract logic thoroughly, as a bug could drain the sponsorship fund. Tools like Safe{Wallet} for smart accounts and Candide's Account Kit can accelerate development of these gasless experiences.

Traditional blockchain onboarding requires users to manage a seed phrase and a wallet extension, creating significant friction. To enable gasless transactions, you first need a way to identify and authorize a user without them needing a funded wallet. This is achieved by integrating a social login provider (like Google, X, or GitHub) or passkeys (WebAuthn). Services like Privy, Dynamic, Magic, and Web3Auth provide SDKs that handle this abstraction, generating a blockchain account for the user upon successful authentication. The user's social account or device biometrics become the key to their on-chain identity.

When a user signs in, the provider creates a smart contract wallet (like an ERC-4337 account) or a custodial key pair on their behalf. Crucially, this initial account has no native tokens (e.g., no ETH on Ethereum). The authentication session generates a cryptographic signature that proves the user's identity to your application's backend, allowing you to sponsor their subsequent transactions. This model shifts the security model from user-managed keys to the security of the OAuth provider or the user's device.

For developers, integration typically involves installing an SDK, configuring OAuth clients, and handling the authentication callback. For example, using Privy, you initialize the client and embed a login button. Upon login, you receive a verified user object containing their blockchain address. This address is the entry point for your gasless system. It's essential to choose a provider that supports the chains you target and offers the right custody model—whether non-custodial via embedded wallets or custodial for maximum simplicity.

This step fundamentally changes the user experience. Instead of "Create a wallet, secure a phrase, fund it," the flow becomes "Sign in with Google." The generated address is immediately usable for gasless actions because your application will act as a paymaster, covering transaction fees. The user's first interaction with the chain can be a mint, a vote, or a follow—all without ever thinking about gas fees or network tokens, removing the primary barrier to entry.

A paymaster is a smart contract that holds funds and agrees to pay for gas on behalf of users. For a gasless onboarding flow, you typically use a verifying paymaster. This type of paymaster validates a user's signature on a UserOperation before sponsoring the transaction, ensuring only authorized interactions are funded. You can deploy your own paymaster contract or integrate with a managed service like those offered by Pimlico, Stackup, or Biconomy, which abstract away much of the complexity.

Integration involves two main parts: the on-chain contract and the off-chain service. The contract defines the sponsorship logic (e.g., which sender addresses or callData are allowed). The off-chain service, often an RPC endpoint provided by the paymaster service, returns a paymasterAndData field. This field is appended to the UserOperation and contains the paymaster's address and a signature proving its intent to pay, which the bundler will verify.

Here is a basic example of generating a UserOperation with Pimlico's Verifying Paymaster via their Bundler RPC:

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const userOp = await smartAccountClient.buildUserOperation({
  transactions: [{
    to: '0x...',
    value: 0n,
    data: '0x...'
  }]
});

// The Pimlico client automatically appends paymasterAndData
const opHash = await smartAccountClient.sendUserOperation(userOp);

In this code, the paymaster service is configured in the SmartAccountClient initialization, handling sponsorship seamlessly.

You must fund your paymaster with the native token of the chain (e.g., ETH on Ethereum, MATIC on Polygon). Managed services provide a dashboard to deposit funds and monitor spending. It's critical to implement rate limiting and whitelisting logic in your paymaster's validation rules to prevent abuse. For example, you might only sponsor gas for transactions that call a specific mint function on your contract during a promotional period.

Finally, test your integration thoroughly on a testnet. Submit UserOperations through your bundler and verify the paymaster covers the gas while the user pays nothing. Monitor events like UserOperationRevertReason to debug failed transactions. A correctly integrated paymaster is invisible to the end-user, creating the seamless, gas-free experience essential for onboarding.

The fee transition model is the logic that determines when and how a user begins paying for their own transaction gas. A common pattern is a graduated subsidy, where the protocol covers 100% of costs initially, then reduces its sponsorship over time or after a usage threshold is met. For example, a dApp might sponsor the first 10 transactions, cover 50% of the next 10, and then require the user to pay 100% thereafter. This model incentivizes initial exploration while ensuring long-term protocol sustainability.

Implementing this requires tracking user state on-chain. A simple Solidity approach uses a mapping to a struct storing a user's transaction count and current subsidy rate. The sponsoring contract's validatePaymasterUserOp function in ERC-4337 would check this state to decide how much of the gas to pay.

solidityCopy
struct UserSponsorship {
    uint256 txCount;
    uint256 subsidyRate; // e.g., 10000 for 100% (using basis points)
}
mapping(address => UserSponsorship) public userSponsorships;

The paymaster logic would calculate its contribution as (gasCost * subsidyRate) / 10000 and revert if the user's wallet doesn't cover the remainder.

Key design decisions include choosing the transition trigger. This can be based on:

• Transaction Count: Simple but may not reflect user commitment.
• Gas Expenditure Total: Tracks actual cost to the sponsor.
• Time-Based Phase-Out: E.g., full subsidy for the first week.
• Hybrid Models: Combining factors for more nuanced control. The trigger must be verifiable on-chain within the paymaster's validation logic to prevent exploitation.

For a smooth user experience, the transition should be communicated clearly within the dApp's UI. Use wallet notifications or in-app modals to warn users before they are required to hold gas tokens. The frontend should also be able to query the user's current sponsorship state (e.g., remainingSponsoredTxs) from the smart contract to display progress.

Finally, consider re-engagement mechanics. Allow users to regain sponsorship through specific actions like providing liquidity, holding a governance token, or completing educational quests. This turns the fee transition from a hard cutoff into a dynamic system that rewards ongoing participation and aligns user incentives with protocol growth.

A gasless onboarding flow allows users to interact with a dApp without holding the native blockchain token (e.g., ETH) to pay for gas. The core mechanism is the meta-transaction, where a user signs a message off-chain, and a relayer (often the dApp backend) submits the transaction and pays the gas fee. This requires a smart contract that can accept a signed message and execute the intended logic on the user's behalf, typically via the executeMetaTransaction function pattern. For a more robust and standardized approach, developers are increasingly adopting ERC-4337 (Account Abstraction), which introduces UserOperation objects and a dedicated mempool.

The first step is to design the smart contract that will process the gasless request. Using a minimal example, we create a GaslessOnboarding contract with a executeMetaTransaction function. This function must verify the user's signature, decode the intended function call from the signed data, and execute it using low-level call. Critical security measures include replay protection (using a nonce) and ensuring only a trusted relayer can call the function. For production, consider using established libraries like OpenZeppelin's MetaTransaction utilities or building a ERC-4337-compliant Smart Contract Account.

On the frontend, the flow begins when a user triggers an action. Instead of creating a standard transaction, your dApp constructs the calldata for the target function and packages it into a meta-transaction object. This object includes the user's address, the contract address, the calldata, and a nonce. The user then signs this structured message using their wallet (e.g., via eth_signTypedData_v4). The signature, along with the meta-transaction data, is sent to your backend relayer service. A common library for handling this signature process on the client side is @metamask/eth-sig-util.

The backend relayer is a critical service responsible for receiving the signed meta-transaction, performing final validation, and submitting it to the blockchain. It must check the signature's validity and the current nonce. If valid, it calls the executeMetaTransaction function on the contract, paying the gas fee from a funded relayer wallet. For scalability and reliability, the relayer should monitor gas prices and may implement a queue. In an ERC-4337 system, the relayer is replaced by a Bundler, which packages UserOperations and submits them to a dedicated EntryPoint contract.

To complete the flow, the dApp must provide user feedback. After the signed request is sent to the relayer, the frontend should poll for the transaction receipt using the transaction hash returned by the relayer. Display the transaction status (pending, confirmed, failed) and, upon success, update the UI to reflect the completed onboarding action. For a better user experience, consider integrating transaction notification services or using WebSocket subscriptions to blockchain nodes for real-time updates.

A successful gasless flow hinges on a secure and efficient relayer backend. This server must validate user requests, manage sponsorship policies (like whitelists or credit systems), and submit the sponsored transactions. For production, implement robust error handling, nonce management to prevent replay attacks, and a monitoring system for gas usage and failed transactions. Consider using a service like Gelato Network or OpenZeppelin Defender to automate and secure this process, rather than building your own infrastructure from scratch.

On the frontend, the user experience is paramount. Integrate a wallet connector like RainbowKit or ConnectKit to detect support for eth_sendRawTransaction and the user's preferred Paymaster. Clearly communicate each step of the meta-transaction process—signing, relaying, and confirmation—to the user. Provide fallback options, such as a direct transaction with the user's own funds, in case the gasless service is temporarily unavailable. Testing with wallets like MetaMask, Coinbase Wallet, and Rabby is essential.

To proceed, start with the UserOperation standard defined by ERC-4337 (Account Abstraction). This provides a unified interface for gasless transactions. Explore SDKs and tools from projects like Stackup, Biconomy, and Alchemy to accelerate development. Their documentation offers starter kits and guides for integrating with various Paymaster services and Bundlers. Remember to audit your sponsorship logic and set appropriate limits to prevent economic attacks on your relayer.

The final step is to deploy and iterate. Begin on a testnet (like Sepolia or Goerli) using test Paymaster services that provide free credits. Monitor metrics such as onboarding conversion rates, average sponsorship cost, and transaction success rates. Use this data to refine your sponsorship rules and UX. A well-designed gasless flow removes a major barrier to entry, significantly improving user acquisition and retention in your Web3 application.