Arbitrum in two minutes, properly

I've set Arbitrum up for enough people now that I know exactly where they get stuck. The network-adding part is easy. The "wait, why did my swap cost 30 cents when you said it would be pennies" part is where the confusion starts — and that's mostly because Arbitrum's fees follow Ethereum mainnet, which catches everyone off guard. I'll get to that. First, get connected.

One thing to know before you start: there are two Arbitrum chains — Arbitrum One (chain ID 42161) is where all the DeFi and GMX live, and Arbitrum Nova (42170) is a cheaper side chain for gaming and social. You want One.

One-click via Chainlist

Same trick as Base, and it's what I default to now:

Go to chainlist.org and hit "Connect Wallet."
Search Arbitrum.
Find the row that says Arbitrum One with chain ID 42161.
Click "Add to MetaMask," approve the prompt, then approve "Switch to Arbitrum One."

The network selector flips over and you're done. Pick the verified row with the most connections — Nova will show up in the same search, so double-check the chain ID before you click.

Manual RPC details

If you'd rather type it yourself, MetaMask → network selector → "Add a network" → "Add a network manually," then enter:

Network name: Arbitrum One
RPC URL: https://arb1.arbitrum.io/rpc
Chain ID: 42161
Currency symbol: ETH
Block explorer: https://arbiscan.io

Save and switch. If the official RPC feels slow or refuses, https://arbitrum-one.publicnode.com is a reliable public backup. The block explorer field matters — with Arbiscan in there, every transaction in MetaMask gets a "View on explorer" link, which makes your life much easier when something looks weird.

Fund it — and budget for gas

Once you're connected, the wallet shows 0.0 ETH. Same as Base: your existing ETH is on whatever network it started on. You need to move some ETH onto Arbitrum. Withdraw from an exchange directly to the Arbitrum network if they support it (cheapest), or bridge from mainnet.

Plan on keeping $5 to $10 of ETH on Arbitrum for gas — that 0.002 to 0.005 ETH covers a few dozen ordinary transactions. Swaps run a touch higher than Base here, usually $0.005 to $0.03, and GMX position changes are in the $0.10 to $0.50 range, so $5 still lasts ages. The full breakdown lives in my gas reserve guide.

The fee quirk that confuses everyone

Here's the thing I have to explain most often. Arbitrum fees aren't set by Arbitrum activity alone. Every transaction on Arbitrum pays an "L1 data fee" — a slice of the cost of posting data to Ethereum mainnet. So when Ethereum mainnet gwei spikes (ETF news, a big mint, one of those days), your Arbitrum fees climb too, even if Arbitrum itself is half-empty.

I've seen a swap that should've been $0.005 come through at $0.04 because mainnet gwei tripled between me clicking and the transaction landing. It's not a bug. I wrote a whole Arbitrum fee explainer about it, but the short version: on a normal day fees are pennies; when mainnet is congested they swell to a few dimes. The live Arbitrum tracker shows the current number before you sign.

Quick sanity check before you trade

Before your first swap on Uniswap or Camelot, open the Arbitrum gas calculator and note the current cost. If the wallet quotes something wildly higher mid-transaction, mainnet probably just spiked — you can wait an hour and it usually settles back. And if GMX or perps are your reason for coming to Arbitrum in the first place, the GMX fee breakdown walks through what a leveraged trade actually costs all-in. Setup done. Welcome to the chain that does DeFi in quarter-seconds for pennies — most of the time.