SubCircle

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:

1. Gas-Free Experience

• No need for users to hold ETH for gas
• All gas costs are paid in USDC via Circle’s Paymaster
• EIP-2612 permit integration for frictionless, gasless approvals

1. Smart Account Management

• ERC-4337-compliant smart wallets for every user
• No need to manage or juggle native tokens
• Enhanced security through smart contract accounts
• Backend-managed deployment and interaction flow per user

1. Subscription Automation

• Reliable automation via Chainlink Automation
• Decentralized execution of performUpkeep calls
• Configurable and autonomous payment cycles
• Built-in logic for subscription status tracking and renewal

Technical Implementation

• Contracts developed using Solidity and Foundry
• Account abstraction implemented via EcdsaKernelAccount
• Circle Paymaster used to cover gas in USDC
• EIP-2612 permit signatures constructed with viem for gasless approvals
• Subscription contracts are deployed per-user via backend logic in Node.js

Key Features

• One-click USDC subscription flow
• Fully gasless from onboarding to payment
• Chainlink-based recurring payment triggers
• Decentralized subscription contract per user
• Real-time USDC balance and payment status tracking
• Modular architecture designed for multi-use integration

Benefits For Users:

• No gas fees
• No need to manage multiple tokens
• Seamless Web2-style subscription experience with Web3 benefits

Future Potential

• Cross-chain subscription support
• Multi-token recurring payment logic
• Tiered and usage-based pricing models
• Integration with Web3 creators, DAOs, and marketplaces
• DAO-native features like recurring treasury allocations

Built 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.

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.