Trying a DeFi protocol on Arbitrum Sepolia, step by step

What Arbitrum Sepolia is

Arbitrum One runs on top of Ethereum: it executes transactions on its own and posts them to Ethereum, which keeps the final record. Arbitrum Sepolia is its test network. It runs the same software, but posts to Sepolia, the test network of Ethereum, instead of to Ethereum itself.

Its coin is ETH, as on Arbitrum One, but test ETH: faucets hand it out free, and it is not meant to be worth anything. Developers put their contracts there before the main network, and anyone can try those contracts without risking money.

A testnet and a mainnet differ in one thing that matters. On a mainnet, coins are money, and a mistake costs money. On a testnet, the wallet, the signatures, the fees and the explorer all work the same way, and the coins are free. That is what makes it the place to learn.

Network details

These are the values a wallet asks for when a network is added by hand. They are the published values of Arbitrum Sepolia:

The chain ID is how a wallet tells networks apart. 421614 is Arbitrum Sepolia; 42161 is Arbitrum One; 11155111 is Sepolia, the test network of Ethereum itself. The names are alike, the networks are not, and a transaction on one of them does not exist on the others.

1. A wallet for testing

Install MetaMask from its own site, as a browser extension on a computer or as the app on a phone, and create a new wallet. Write its seed phrase, which MetaMask calls the Secret Recovery Phrase, on paper and keep it to yourself: whoever has it controls the wallet on every network, test or not.

If you already keep real funds in MetaMask, use a separate wallet for testing. Other wallets work as well; the holder account names the ones it knows on its first screen.

2. Add Arbitrum Sepolia to MetaMask

There are two ways. The short one is to let the holder account do it (step 4). When a wallet comes in on another network, the page names both networks and offers a button, Switch to Arbitrum Sepolia. MetaMask then asks you to approve adding the network, if it has never seen it, and switching to it.

By hand: open the list of networks in MetaMask, choose to add a network, and fill in the five values from the table above. Some wallets hide test networks until you turn them on in their settings.

3. Test ETH from an Arbitrum Sepolia faucet

Every transaction costs a little ETH for gas, on a test network as on a main one. Nobody can make more of a network’s own coin, so test ETH comes from public faucets: sites that hand out a small amount to anyone who asks.

Three faucets give ETH on Arbitrum Sepolia: QuickNode, Alchemy and Chainlink. Each is somebody else’s site and sets its own terms: how much, how often, and what it asks of you. Some ask nothing of a new wallet; some ask that the address hold a little real ETH on Ethereum, as a check against bots. If one refuses, try another.

A little is enough: a transaction on Arbitrum costs a tiny fraction of what a faucet gives. The Test funds screen of the holder account shows how much ETH your address holds and links the same faucets.

4. Enter the holder account

Open the holder account in the browser where MetaMask is installed and press Connect MetaMask. Connecting gives the page your address and nothing to sign; the wallet asks you to allow the site.

On a phone, the same page offers to open itself inside the wallet app. Before you connect, every screen can be looked at without a wallet, with figures from an hourly snapshot.

If the wallet is on another network, press Switch to Arbitrum Sepolia (step 2). From then on every figure on the page is read from the contract through your own wallet.

5. Take test stablecoins

Open the Test funds screen. The currencies of this deployment are test tokens made for it: tUSDC, tUSDT and tDAI take deposits; tWETH and tWBTC are dormant for now and take none. One press hands out 10,000 tUSDC, tUSDT or tDAI. Each press is a transaction, so it needs a little test ETH.

One daily limit covers every address and every currency together. It starts again at midnight UTC and grows as the protocol moves through its stages. If a press is refused, less is left of today’s limit than it hands out; come back after midnight UTC.

6. Open a position

Open the Mint screen, choose tUSDC, tUSDT or tDAI and enter an amount; the smallest deposit is one unit. Before anything is signed, the screen shows where the deposit falls on the curve of the current stage, what is withheld as the issuance fee, and how many ASTRX the position will hold.

Then two signatures. The first, Allow, lets the contract take that currency from your address: a token contract moves nothing without it. The second, Deposit, creates the position in the same transaction. A position holds your collateral and the ASTRX minted against it.

7. Then try the rest

With a position open, the other screens have something to work on. Each of these takes one or two signatures:

• Redeem part of a position. On the Positions screen, Split divides a position into equal parts; Redeem gives one part’s collateral back in full, with no fee.
• Close a position. Close into tokens hands its ASTRX to your address. The screen says beforehand what closing gives: when the collateral behind a position is below the backing per token, a share of its tokens is withheld for the reserve, and a large position may have to be closed in parts.
• Buy or sell ASTRX. The Market screen trades in the ASTRX/tUSDC pool on Uniswap v3, through the Assetrix router: first allow the router, then buy or sell.
• Vote. The Vote screen holds thirteen questions about the parameters of the protocol. Voting with tokens burns them for good; voting with credits, which closing a position can earn, burns nothing.
• Send. The Transfer screen sends ASTRX, or hands a whole position, to another address. A transfer cannot be taken back.
• Redeem tokens. The Redeem screen hands ASTRX back for a share of the reserve, less the redemption fee.

Every message that reports a finished step carries a link, Look at it in the explorer: the transaction on sepolia.arbiscan.io, with its hash, its block and what it moved. That link is the record of the step.

If something does not work

• Nothing can be signed. The address holds no test ETH. Take some from a faucet (step 3).
• Arbitrum Sepolia is not in the list of networks. Let the holder account add it, or add it by hand with the values above. Some wallets hide test networks until you turn them on.
• The page says the wallet is on another network. Arbitrum One and Sepolia are other networks. Press Switch to Arbitrum Sepolia.
• Test funds refuses a press. Less is left of today’s shared limit than the press hands out. The limit starts again at midnight UTC.
• A deposit in tWETH or tWBTC is refused. Both are dormant and take no deposits yet. Use tUSDC, tUSDT or tDAI.
• A faucet refuses. Each faucet sets its own terms. Try another, or come back when its waiting time has passed.
• Closing gives less than you expected. The Positions screen says why: a dilution fee, or a limit on closing for now. Redeeming the position still gives its collateral back in full.