Blockchain Developer
Blockchain and DeFi questions
147 questions on Blockchain and DeFi for blockchain developers, easiest first.
Easy 42
- Keys and addresseseasy
- What links one block to the nexteasy
- The account nonceeasy
- Token decimalseasy
- When a block is finaleasy
- What a rollup doeseasy
- How proof of stake secures the chaineasy
- The Merkle root in a blockeasy
- What the mempool iseasy
- Hot vs cold walleteasy
- How USDC keeps its valueeasy
- Why contracts need oracleseasy
- Reading a transaction on a block explorereasy
- How often Ethereum makes a blockeasy
- The Bitcoin halvingeasy
- A 2-of-3 multisig walleteasy
- Coins held on an exchangeeasy
- What makes a flash loan possibleeasy
- What a zero-knowledge proof showseasy
- Running your own validatoreasy
- What the contract ABI is foreasy
- How an AMM sets priceseasy
- What a lock-and-mint bridge doeseasy
- Why Ethereum moved to proof of stakeeasy
- Bitcoin's UTXO modeleasy
- What a 51% attack allowseasy
- What "Connect wallet" shareseasy
- Where NFT images usually liveeasy
- How a DAO usually voteseasy
- Layer 1 vs layer 2easy
- Cost of reading a view functioneasy
- Mixed-case Ethereum addresseseasy
- What TVL measureseasy
- Why WETH existseasy
- Tokens sent to the token's own addresseasy
- A stablecoin pool paying 40%easy
- What front-running iseasy
- A suspicious NFT approvaleasy
- Using a DEX price directlyeasy
- What a flash loan iseasy
- What a sandwich attack iseasy
- Old unlimited approvalseasy
Medium 52
- Front-running a swapmedium
- Blobs and rollup feesmedium
- Reading vs writing with viemmedium
- When to show "payment received"medium
- Showing a user's historymedium
- Chain ID in transactionsmedium
- Working out a transfer feemedium
- Sending 1.5 USDC in base unitsmedium
- Choosing slippage tolerancemedium
- Computing a health factormedium
- Multiple browser wallets fightingmedium
- What an L2 sequencer doesmedium
- How an upgradeable proxy worksmedium
- Speeding up a stuck transactionmedium
- Later transactions all stuckmedium
- Shares minted by an ERC-4626 vaultmedium
- Loading 40 token balances fastmedium
- Showing an ENS name safelymedium
- When the RPC provider goes downmedium
- Market cap vs fully diluted valuemedium
- APR vs APYmedium
- A positive funding ratemedium
- How far a 10x position can fallmedium
- Using a pull-based oraclemedium
- Same seed, different addressmedium
- Losing precision with Numbermedium
- Tokens vested after 18 monthsmedium
- Fee earned on a swapmedium
- Why algorithmic stablecoins can collapsemedium
- "Cannot estimate gas" before sendingmedium
- Filtering events by usermedium
- Querying a protocol's historymedium
- Asking the wallet to switch networkmedium
- Effective gas price with a fee capmedium
- Where Solana keeps program statemedium
- Validium vs rollupmedium
- The extra risk of restakingmedium
- Blind signing on a hardware walletmedium
- stETH vs wstETHmedium
- Why governance uses a timelockmedium
- A transaction that was replacedmedium
- Building Sign-In with Ethereummedium
- Balance not updating after a swapmedium
- Reading a balance from last yearmedium
- A transfer fee in rupeesmedium
- Lowering an allowance Bob can seemedium
- A swap with no minimum outputmedium
- A swap that executes much latermedium
- Hiding a trade from botsmedium
- Mixing oracle and token decimalsmedium
- Casting a negative pricemedium
- Address poisoningmedium
Hard 53
- Lending protocol price oraclehard
- First depositor in a vaulthard
- Rollup withdrawal timeshard
- Account abstractionhard
- Constant product swap outputhard
- Trade-offs of a TWAP oraclehard
- Checking a Chainlink pricehard
- Flash-loaned voting powerhard
- Indexer shows phantom depositshard
- Using block.number for time on L2hard
- Trusting a cross-chain messagehard
- Missing account checks on Solanahard
- Why ZK rollups still post datahard
- Impermanent loss at a 4x price movehard
- Collateral seized in a liquidationhard
- The forgotten implementation contracthard
- Building leaves for a Merkle airdrophard
- Concentrated liquidity out of rangehard
- Why the first storage write costs mosthard
- A private key in a NEXT_PUBLIC variablehard
- Changing an allowance from 100 to 50hard
- When collateral can be frozenhard
- A lookalike address in the historyhard
- Who actually builds Ethereum blockshard
- One liquid staking protocol gets too bighard
- Borrow rate above the kinkhard
- How a lending pool gets bad debthard
- Liquidity leaves when rewards endhard
- LP tokens minted on deposithard
- A proposal passed at 3amhard
- The real trust in a bridgehard
- A compromised npm package in a dapphard
- Drained after "just signing a message"hard
- Holding a rebasing token in a poolhard
- Scaling a price feed correctlyhard
- Trading through intentshard
- Why an L2 fee spikedhard
- The trusted setup in a SNARKhard
- Signing payouts from a backendhard
- Pricing USDC at exactly $1hard
- Admin check fails for the real adminhard
- Why stablecoin pools use StableSwaphard
- Is block.timestamp safe to usehard
- The first depositor attackhard
- Reward rate from the token balancehard
- A permit that someone uses firsthard
- Oracle prices after an L2 outagehard
- How far one swap moves a pool pricehard
- Deploy then initialise in two transactionshard
- A flash loan callback anyone can triggerhard
- Rewards while nobody is stakedhard
- Trading ahead of an oracle updatehard
- A position that cannot be liquidatedhard