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I've been building on Arc Testnet for the past few days and wanted to share what I came up with — 

, a DeFi app I built entirely from scratch. No forks, no templates, just me figuring things out one error at a time.

It was honestly pretty challenging at points. Arc Testnet has some quirks that aren't immediately obvious, and there were moments where I genuinely didn't know if something was broken on my end or the network's. But I got through it and learned a lot in the process.

USDC and EURC swaps on Arc Testnet via a custom AMM contract I wrote in Solidity. The contract manages two liquidity pools and exposes a 

 function for real-time price estimation before the user commits to a transaction.

The trickiest part here wasn't the contract it was MetaMask. Arc's RPC doesn't always respond to MetaMask's receipt polling in time, so 

 would just hang indefinitely. I ended up replacing it with a custom polling function that queries the Arc RPC directly every 2 seconds until the receipt comes back. Once I figured that out, everything became stable.

I also had to write a separate script to seed the pool with liquidity before swaps could work. The pool currently holds 100 USDC and 49 EURC.

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Cross-chain USDC transfers between Arc Testnet and Ethereum Sepolia using Circle's CCTP V2. The flow is: approve USDC to the CCTP contract, call 

 on the source chain, wait for Circle's attestation service to sign the burn proof, then call 

 on the destination chain to mint. No wrapped tokens, no intermediary holding your funds.

This is the part I'm most proud of. It's a trustless on chain escrow system built around a simple idea: two parties that don't fully trust each other can still transact safely if there's a smart contract in the middle.

The flow works like this. The sender calls 

 and locks USDC or EURC in the contract along with a description of what they're paying for and the address of a pre-agreed arbiter. The recipient delivers their side of the deal. If the sender is happy, they call 

 and the funds are released instantly. If something goes wrong, either party can call 

 and the arbiter steps in they can either release the funds to the recipient or refund the sender.

The contract tracks four states: PENDING, COMPLETED, REFUNDED, and DISPUTED. Every transition is on-chain and irreversible. No platform fees, no middleman, just the contract enforcing what both parties agreed to upfront.

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The dashboard reads USDC and EURC balances directly from the token contracts on both Arc Testnet and Ethereum Sepolia using ethers.js v6 no backend, no indexer. The history page pulls transaction data from the Arc API and refreshes automatically.

A few other things I ran into while building

 and breaks if you add that flag globally. Took me longer than I'd like to admit to track that one down.

Gas estimation on Arc also occasionally undershoots for freshly deployed contracts, so I ended up hardcoding gas limits 100k for approvals, 200k for swaps and escrow interactions  just to keep things predictable.

Contracts on Arc Testnet (Chain ID: 5042002)

 React.js, ethers.js v6, Solidity 0.8.19, Hardhat, Circle CCTP V2, Netlify

If you want to try it out, add Arc Testnet to MetaMask and grab some tokens from the faucet. Would love to hear any feedback, especially on the escrow flow. Happy to answer questions about any of the technical decisions too.

ArcPulse Swap, Bridge, and Escrow on Arc Testnet (built from scratch)

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