Definition
A paymaster is an ERC-4337 helper contract that agrees to pay the network fee for a user operation instead of requiring the sending account to pay it directly.
How a paymaster sponsors an operation
The user operation identifies a paymaster and supplies the data it needs. The ERC-4337 EntryPoint calls the paymaster during validation to determine whether it accepts the operation. The paymaster must maintain a sufficient deposit with the EntryPoint to cover accepted operations.
A paymaster can apply conditions such as an approved account, action, campaign or spending policy. Some implementations sponsor the entire fee, while others recover the cost from the user in another token.
Someone still pays the fee
Gasless describes the user experience, not the economics. The paymaster pays the network fee first, and the application may subsidize that cost or recover it separately.
A paymaster may reject an operation, run out of available deposit or support only selected accounts and actions. Applications should not assume sponsorship until validation succeeds.
What it does not mean
A paymaster pays or sponsors execution fees. A bundler collects user operations and submits them for execution. A smart account authorizes the requested action. These are separate ERC-4337 roles.
Where this term fits
Questions about paymaster
- Does a paymaster make every transaction free?
- No. It can remove the requirement for the sender to pay in the network native token, but the paymaster or another party still bears the fee.
- Can a paymaster charge the user in another token?
- Yes. An implementation may charge an ERC-20 token or use another reimbursement model, subject to its validation and accounting logic.
- Can a paymaster refuse an operation?
- Yes. It validates each request against its own sponsorship conditions and can reject requests that do not qualify.
See these concepts in context
Review the Fensory MCP connection, tools and account controls.