SubCircle

Problem Statement

SubCircle is a decentralized subscription payment protocol designed to transform recurring payments in Web3. Built on Arbitrum Sepolia, it leverages Account Abstraction (ERC-4337) and Circle’s Paymaster to enable seamless, gasless USDC subscriptions. SubCircle addresses three core challenges in Web3-based subscriptions:Gas-Free ExperienceNo need for users to hold ETH for gasAll gas costs are paid in USDC via Circle’s PaymasterEIP-2612 permit integration for frictionless, gasless approvalsSmart Account ManagementERC-4337-compliant smart wallets for every userNo need to manage or juggle native tokensEnhanced security through smart contract accountsBackend-managed deployment and interaction flow per userSubscription AutomationReliable automation via Chainlink AutomationDecentralized execution of performUpkeep callsConfigurable and autonomous payment cyclesBuilt-in logic for subscription status tracking and renewalTechnical ImplementationContracts developed using Solidity and FoundryAccount abstraction implemented via EcdsaKernelAccountCircle Paymaster used to cover gas in USDCEIP-2612 permit signatures constructed with viem for gasless approvalsSubscription contracts are deployed per-user via backend logic in Node.jsKey FeaturesOne-click USDC subscription flowFully gasless from onboarding to paymentChainlink-based recurring payment triggersDecentralized subscription contract per userReal-time USDC balance and payment status trackingModular architecture designed for multi-use integrationBenefits For Users:No gas feesNo need to manage multiple tokensSeamless Web2-style subscription experience with Web3 benefitsFuture PotentialCross-chain subscription supportMulti-token recurring payment logicTiered and usage-based pricing modelsIntegration with Web3 creators, DAOs, and marketplacesDAO-native features like recurring treasury allocationsBuilt at ETH Taipei Hackathon 2025, SubCircle aims to close the UX gap between traditional and Web3 subscription systems by delivering a secure, automated, and gasless recurring payment experience.

Solution

I built a USDC-based subscription system on Arbitrum Sepolia using smart wallets, Circle’s Paymaster, and viem. The goal was to enable gasless, recurring payments where users can subscribe to content creators and optionally send USDC tips—without needing ETH for gas.I used Foundry to write and test the smart contracts, and handled all off-chain logic in Node.js using viem. This includes account abstraction via ERC-4337, EIP-2612 permit signing, and userOp construction. Each user gets their own deployed Subscription contract, which keeps the system modular and customizable.For gas sponsorship, I integrated Circle’s Paymaster, constructed the paymasterData manually with permit signatures, and estimated postOpGas directly from the Paymaster contract. This allowed me to pack everything into a single userOp and submit it through Pimlico’s bundler.One particularly hacky part was manually encoding the entire flow using low-level viem utilities—no abstractions, just raw permit + packed data + bundled ops.I'm also integrating Chainlink Automation to periodically trigger performUpkeep() on each user’s Subscription contract, enabling fully automated, decentralized renewals.