These are the questions beginners ask most often about blockchains, fees, transactions and safety. Each answer is short and links to a longer article. Unknown words are explained in the glossary.
Frequently asked questions
What is a blockchain?
A blockchain is a shared record of transactions that many computers keep in sync. Transactions are grouped into blocks, and each block contains the hash of the previous one, which links them in a chain. See what is a blockchain.
What is the difference between Bitcoin and Ethereum?
Bitcoin focuses on being digital money and uses proof of work. Ethereum also supports smart contracts, which are programs that run on the chain, and uses proof of stake. They have different coins, address formats and fee systems.
What is a layer 2?
A layer 2 is a network that runs on top of a layer 1 such as Ethereum. It processes transactions more cheaply and posts the data back to the L1. Arbitrum, Base and OP Mainnet are examples. See layer 1, layer 2 and layer 3.
Is Polygon a layer 2?
Polygon PoS is commonly called one, but it is technically a sidechain with its own validators. It is not a rollup, so it does not inherit Ethereum's security in the same way.
What does a node do?
A node is a computer that runs the blockchain software, stores the chain and checks that every block follows the rules. Wallets and apps usually talk to nodes through an RPC endpoint.
What is gas?
Gas is the unit that measures how much work a transaction needs on an EVM chain. You pay for it in the chain's coin, such as ETH. See gas and fees.
Why do fees change so much?
Blocks have limited space, so when many people want to transact, they bid higher to be included. Fees also differ between chains because of their design. See why fees differ between chains.
Which chain is the cheapest for sending money?
It changes from hour to hour. Layer 2 networks and Solana are usually far cheaper than Ethereum, but check the live numbers on the gas tracker. Our guide on the cheapest way to send USDC explains how to compare.
Why does sending a token cost more than sending ETH?
A token transfer runs smart contract code and updates stored balances, which uses more gas than a simple coin transfer. See stablecoins.
What is a gwei?
A gwei is one billionth of an ETH. Gas prices on Ethereum and its layer 2 networks are quoted in gwei.
Why is my Bitcoin transaction stuck?
Its fee rate is probably too low compared with other waiting transactions in the mempool, so miners pick others first. You can wait, or use a wallet feature that raises the fee. See Bitcoin mempool and fees.
What is the mempool?
It is the waiting area of transactions that were sent but are not yet included in a block.
How long does a transaction take?
It depends on the chain. Solana confirms in seconds, Ethereum blocks come every 12 seconds, and Bitcoin blocks come about every 10 minutes. Final settlement takes longer than the first confirmation. See finality and confirmations.
What does finality mean?
Finality is the point where a transaction can no longer be reversed in practice. Different chains reach it after different amounts of time.
Can a transaction be reversed?
No. Once a transaction is final, nobody can undo it, including the network and ChainMonitor. Always check the address and network before you send.
How do I read a transaction?
A transaction page shows who sent it, who received it, the amount, the fee, the block and the status. See read a transaction, then paste a hash into the search at the top of the site.
What is a seed phrase?
A seed phrase is a list of 12 or 24 words that can restore all the keys in a wallet. Anyone who has it can take your funds, so keep it offline and never type it into a website. See wallets and keys.
Is a wallet the same as an exchange account?
No. At an exchange, the company holds your keys. In a self-custodial wallet, you hold them yourself. The second gives you control and also full responsibility.
Can I use the same address on Ethereum and Base?
Yes. Ethereum, Arbitrum, Base, Optimism and Polygon share the EVM address format, so one address works on all of them. Balances are separate on each chain. Bitcoin and Solana use different address formats.
What happens if I send crypto on the wrong network?
It depends. If you control the same address on that network, you can usually still reach the funds by switching networks in your wallet. If it went to an exchange or another person that does not support it, recovery may be hard or impossible.
What is a stablecoin?
A stablecoin is a token designed to keep a steady value, usually one US dollar. USDC and USDT are common examples. See stablecoins.
What is the difference between USDC and USDC.e?
USDC is issued directly on a chain by its issuer. USDC.e is a bridged copy created through a bridge. Some apps accept only one of them.
What is a bridge?
A bridge moves value between two blockchains, usually by locking tokens on one chain and creating matching tokens on the other. See bridges and their risks.
Why do withdrawals from Arbitrum, Base and Optimism take 7 days?
They are optimistic rollups, which allow a challenge window of about 7 days before withdrawals through the official bridge are final. Fast bridges can shorten the wait for a fee. See optimistic vs zk rollups.
Is crypto safe?
The networks themselves have a strong record, but users face real risks: lost seed phrases, scams, fake websites, risky smart contracts and bridges. Taking basic steps cuts most of them. Nothing here is financial advice.
How can I avoid scams?
Never share your seed phrase, use only links from official sources, be suspicious of urgent messages and offers that seem too good, and read every wallet prompt before signing. Check approvals regularly.
What is a public RPC endpoint and which should I use?
It is a free node address that wallets and apps use to connect to a chain. Speed and reliability vary. See public RPC endpoints and compare them on the RPC health page.
Where can I see blockchains working live?
Open any chain on ChainMonitor, such as Ethereum or Bitcoin, to see new blocks arrive and how full each one is. New to the site? Read how to use ChainMonitor.