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Types of Paymasters

Explore different Paymaster patterns in ERC-4337, from whitelists to token gas payments.

Paymasters in ERC-4337 can be implemented in various ways depending on how gas is sponsored and what validation logic is required. Below are the most common patterns.

✅ Whitelist Paymaster

Simplest model. The Paymaster maintains a list of allowed users or operations.

Use case: Free gas for early users, partners, or test campaigns.

How it works:

  • Checks the sender address or calldata
  • Accepts or reverts in validatePaymasterUserOp
  • Optionally restricts frequency or nonce range

🔐 Verifying Paymaster (Off-Chain Signed)

Requires an off-chain component to approve each transaction.

Use case: Controlled sponsorship via API, rate limits, user-specific logic

How it works:

  • User gets a signed message from a backend
  • paymasterAndData includes the signature and metadata
  • Contract verifies the signature before approving sponsorship

This model is extensible and secure — popular in production wallets.

💰 ERC-20 Paymaster (Token Paymaster)

Lets users pay for gas in an ERC-20 token, which the Paymaster converts to ETH.

Use case: Gasless UX for apps where users hold tokens but no ETH

How it works:

  • Contract checks token balance or transfer approval
  • Performs a token-to-ETH swap off-chain or via internal pool
  • Uses ETH deposit in EntryPoint to cover the gas

Caution: swaps can be complex and require slippage/timing protection.

🧩 Hybrid and Custom Patterns

  • Quota-based Paymasters: Allow N txs per user/day
  • Multi-condition checks: Combine whitelist + signatures
  • Action-specific Paymasters: Only subsidize known callData

The Paymaster model is extremely flexible. The key constraint is ensuring validatePaymasterUserOp() remains safe, bounded, and deterministic.

✅ Summary

Paymasters enable powerful UX flows, from gasless onboarding to pay-in-token systems. Choose a pattern based on your app’s risk tolerance, business model, and infrastructure capabilities.