JP Morgan Chase Blockchain Interview Questions & Answers
Curated interview practice questions with answers. These are practice scenarios, not a verified list of past interview questions.
About JP Morgan Chase hiring for Blockchain roles
JPMorgan Chase is a global bank offering investment banking, commercial banking, asset management and consumer banking through Chase. Its India corporate centres in Mumbai, Bengaluru and Hyderabad support technology, operations, analytics and risk functions. It hires for software engineers, QA engineers, data analysts, data scientists and quantitative analysts.
For Blockchain roles, this JP Morgan Chase practice set focuses most on dApp Development (6), Cryptography for Blockchain (6), Blockchain Fundamentals (5), Consensus and Scaling (4). It has 7 easy, 18 medium, 5 hard questions, so you can start easy and work up to the harder ones.
Company type
Banking & finance
Headquarters
New York, USA
Main India offices
Mumbai, Bengaluru, Hyderabad
JP Morgan Chase Blockchain interview process
Online assessment (coding + aptitude)
Video interview (HireVue style)
Technical round
Hiring manager round
HR round
Typical pattern based on public candidate experiences. Rounds vary by role, team and year.
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A dApp usually has smart contracts on a chain holding core logic and assets; a front-end, often React or Next.js, that connects to the user's wallet; a library such as ethers.js, viem or wagmi to read and write contracts through an RPC provider; an indexer or subgraph for fast queries of history; decentralised storage such as IPFS for files and metadata; and optional back-end services for notifications, relaying or off-chain computation, with oracles bringing external data on-chain.
EIP-1559 splits the fee into a base fee and a priority fee. The protocol sets the base fee per block from demand: if the previous block was more than half full, it rises up to 12.5 percent, otherwise it falls. The base fee is burned. Users add a priority fee (tip) for the proposer and set maxFeePerGas as their cap. They pay base fee plus tip, never more than the cap, which makes fees more predictable.
03
Your dApp's users are paying high gas fees on Ethereum mainnet. How would you choose a Layer 2?
I would compare candidate rollups on security (proof system live, stage of decentralisation, upgrade keys), EVM compatibility so our Solidity code deploys unchanged, ecosystem fit (wallets, oracles, liquidity, bridges our users already use), fees and throughput, and withdrawal experience. I would deploy to testnets first, measure real costs and latency, and check that our dependencies such as Chainlink feeds exist there. Then migrate gradually, keeping L1 contracts for high-value settlement if needed.
04
An HR team wants to store employee records on a blockchain. Would you recommend it?
Usually no. Employee records are owned by one organisation, change often and contain personal data that must be correctable and deletable under the DPDP Act 2023. A normal database with role-based access and audit logs is cheaper, faster and compliant. I would ask who else needs to trust the data. If several employers or background-check agencies must verify certificates, I would store only hashes of credentials on a permissioned chain and keep the actual data off-chain.
05
Tell me about a time you explained blockchain to a non-technical stakeholder.
Situation: a business head wanted 'blockchain' in a vendor portal because competitors mentioned it. Task: help him decide. Action: I compared it to a shared online spreadsheet that nobody can secretly edit, then showed cost, speed and privacy trade-offs against a normal database with audit logs. Result: we agreed to keep the portal on a database and anchor monthly hashes of invoices on a chain for proof, saving months of work while meeting the trust goal.
06
Your fantasy sports contract needs live match scores. How do you get that data on-chain?
Smart contracts cannot call web APIs, so use an oracle. Options include a decentralised oracle network such as Chainlink Functions to fetch from several sports APIs and aggregate, or an optimistic oracle where results are proposed and can be disputed. Settle only after the match result is final, use multiple data sources, add a dispute window for high-value pools, and handle cancelled matches. Avoid a single back-end key posting results, which is a central point of failure.
07
Show how to sign and verify a message with ethers.js.
With ethers v6, a wallet signs using EIP-191 personal sign, and verifyMessage recovers the address.
import { Wallet, verifyMessage } from 'ethers';
const wallet = Wallet.createRandom();
const message = 'Login nonce: 48213';
const signature = await wallet.signMessage(message);
const recovered = verifyMessage(message, signature);
console.log(recovered === wallet.address); // true
This pattern powers Sign-In with Ethereum; the server issues a fresh nonce each time to stop replay.
// script/Deploy.s.sol
pragma solidity ^0.8.24;
import {Script, console} from 'forge-std/Script.sol';
import {Counter} from '../src/Counter.sol';
contract Deploy is Script {
function run() external returns (Counter c) {
vm.startBroadcast();
c = new Counter();
vm.stopBroadcast();
console.log('Counter deployed at', address(c));
}
}
# Run it with an encrypted keystore account
forge script script/Deploy.s.sol --rpc-url $RPC_URL \
--account deployer --broadcast --verify
Broadcast output in the broadcast folder records addresses for later scripts.
IPFS, the InterPlanetary File System, is a peer-to-peer network for storing and sharing files. Instead of locating files by server address, it identifies them by a content identifier (CID) derived from the file's hash, which is content addressing. The same content always has the same CID, and any change gives a new CID, so data cannot be swapped silently. Files must be pinned by a node or pinning service, otherwise they may disappear.
10
Your target users in India have never used crypto wallets. How do you design onboarding?
Hide crypto complexity. Offer login with phone or email using embedded or smart contract wallets, so no seed phrase is needed at first. Sponsor gas with a paymaster so users need no tokens. Show amounts in rupees and plain language, support regional languages, and explain actions in simple terms. Provide account recovery via passkeys or guardians, and let advanced users export to self-custody later. Ensure KYC and tax requirements are clear where money is involved.
11
A stablecoin used as collateral in your protocol loses its peg. How do you respond?
Activate the risk plan: pause new borrowing against that asset and freeze its use as new collateral through governance or the guardian. Switch its oracle to a market price rather than a hard-coded one dollar, so positions are valued honestly, which may trigger liquidations. Reduce its loan-to-value and supply caps. Communicate clearly with users. Longer term, cap exposure per stablecoin, diversify collateral and model depeg scenarios in risk dashboards.
12
How do you verify a signed message inside a Solidity contract?
Recompute the message hash, add the Ethereum signed message prefix, recover the signer and compare it.
import {ECDSA} from '@openzeppelin/contracts/utils/cryptography/ECDSA.sol';
import {MessageHashUtils} from '@openzeppelin/contracts/utils/cryptography/MessageHashUtils.sol';
function verify(address signer, uint256 amount, uint256 nonce, bytes calldata sig) public view returns (bool) {
bytes32 h = keccak256(abi.encode(address(this), block.chainid, amount, nonce));
bytes32 eth = MessageHashUtils.toEthSignedMessageHash(h);
return ECDSA.recover(eth, sig) == signer;
}
Track used nonces to block replays.
13
Write a Python function that computes a Merkle root from a list of transactions.
Hash leaves, then hash pairs until one remains, duplicating the last hash when a level is odd (Bitcoin style).
import hashlib
def h(b):
return hashlib.sha256(b).digest()
def merkle_root(txs):
level = [h(t.encode()) for t in txs]
while len(level) > 1:
if len(level) % 2:
level.append(level[-1])
level = [h(level[i] + level[i+1]) for i in range(0, len(level), 2)]
return level[0].hex()
print(merkle_root(['tx1', 'tx2', 'tx3']))
14
How do you keep up with security and cryptography developments in Web3?
I follow a routine. Weekly I read new audit reports and post-mortems of exploits, and I try to reproduce one in Foundry. I track Ethereum Improvement Proposals and upgrade notes, read Solidity release notes, and practise on capture-the-flag platforms such as Ethernaut and Damn Vulnerable DeFi. I also keep a personal notes file of attack patterns. This keeps my knowledge practical rather than just theoretical, and I share summaries with my team.
15
How do you get the latest block number from an Ethereum node using JSON-RPC?
Send a JSON-RPC POST request to the node or provider URL. The result is a hex string that you convert to decimal.
curl -s -X POST https://rpc.example.org \
-H 'Content-Type: application/json' \
-d '{"jsonrpc":"2.0","method":"eth_blockNumber","params":[],"id":1}'
# Response: {"jsonrpc":"2.0","id":1,"result":"0x15d3a1c"}
# In Python: int('0x15d3a1c', 16)
Other common methods are eth_getBalance, eth_call and eth_getTransactionReceipt.
16
Calculate the output of a swap in a constant product pool with a 0.3 percent fee.
Formula: amountOut = (amountIn x 997 x reserveOut) / (reserveIn x 1000 + amountIn x 997).
Example: reserves 1,000 ETH and 3,000,000 USDC, swap 10 ETH.
amountInWithFee = 10 x 997 = 9,970
numerator = 9,970 x 3,000,000 = 29,910,000,000
denominator = 1,000 x 1000 + 9,970 = 1,009,970
amountOut = 29,615 USDC (approx)
The spot price is 3,000, but the trader gets about 2,961.5 per ETH because of fee and price impact.
17
Write a Foundry invariant test for a token's total supply.
Invariant tests call random functions on target contracts and check a property after every call.
import {Test} from 'forge-std/Test.sol';
import {MyToken} from '../src/MyToken.sol';
import {Handler} from './Handler.sol';
contract SupplyInvariant is Test {
MyToken token;
Handler handler;
function setUp() public {
token = new MyToken();
handler = new Handler(token);
targetContract(address(handler));
}
function invariant_supplyMatchesBalances() public view {
assertEq(token.totalSupply(), handler.sumOfBalances());
}
}
The handler bounds inputs and tracks actors so calls stay realistic.
Modifiers are reusable pieces of code that run before or after a function body, placed where the underscore symbol appears. They are mainly used for checks such as onlyOwner, whenNotPaused or nonReentrant. For example, modifier onlyOwner() { require(msg.sender == owner, 'not owner'); _; } blocks everyone except the owner. Keep modifiers short and check-only; complex logic inside modifiers hides behaviour and increases bytecode size because the code is inlined into every function that uses it.
Slashing is a penalty that burns part of a validator's stake and forcibly exits it when it provably breaks protocol rules. On Ethereum the slashable offences are proposing two different blocks in the same slot and making conflicting or surrounding attestations. The penalty grows if many validators are slashed around the same time, which punishes coordinated attacks. Simply being offline is not slashing; it only causes small inactivity penalties. Running the same key on two machines is the most common cause.
20
How do you read a contract's storage slot directly with Foundry's cast?
Use cast storage with the contract address and slot number. For mappings, compute the slot as keccak256(key . slot).
# Read slot 0 (often the first state variable)
cast storage 0xContractAddress 0 --rpc-url $RPC_URL
# balanceOf mapping stored at slot 2, key = user address
cast index address 0xUserAddress 2
cast storage 0xContractAddress <slot-from-above> --rpc-url $RPC_URL
This shows that private variables are not secret: anyone can read storage.
A Merkle tree hashes data items in pairs, level by level, until one root hash remains. The root summarises all items: changing any item changes the root. A Merkle proof is the list of sibling hashes on the path from one item to the root. With it, a light client can prove that a transaction is in a block using about log2(n) hashes instead of downloading all transactions. Airdrop allowlists use the same trick on-chain.
22
A user's transaction has been pending for an hour. How do you troubleshoot it?
First check it on a block explorer: if it is not found, it was never broadcast. If pending, the fee is probably below current market rates, or an earlier transaction with a lower nonce is stuck and blocking it. On Ethereum you fix it by sending a replacement with the same nonce and a higher max fee and priority fee, or cancel by sending zero ETH to yourself with that nonce. Then make the wallet estimate fees dynamically.
23
A transaction keeps failing with an out of gas error. How do you fix it?
First see whether the gas limit was too low or the function is genuinely unbounded. Run eth_estimateGas or simulate with cast run or Tenderly to see actual gas used and where it fails. If estimation is fine, raise the limit with a buffer of 10 to 20 percent. If the function loops over a growing array, redesign it with pagination or pull-based patterns, because the block gas limit will eventually make it impossible to call.
24
Four organisations are building a private EVM network. Which consensus would you pick: Raft or QBFT?
Raft is crash fault tolerant: fast and simple, but it assumes no node lies, so it fits when all members trust each other's infrastructure. QBFT is Byzantine fault tolerant and tolerates f malicious nodes out of 3f+1, so with four validators it survives one bad actor and gives immediate finality. Since the organisations are separate businesses that may not fully trust each other, I would choose QBFT and run at least four validators, ideally more.
25
You need to send ETH to hundreds of winners. Should you push payments or let them pull?
Prefer pull payments. If a contract pushes ETH in a loop, one recipient that reverts, perhaps a contract without receive, can block everyone, and the loop may exceed the gas limit. With pull payments, the contract records each winner's amount in a mapping and winners call withdraw, which zeroes their balance before sending. This isolates failures and limits reentrancy risk. Push only for small fixed lists using call with a checked result.
26
What is a cryptographic hash function and what properties must it have?
A hash function maps any input to a fixed-size output, such as 256 bits. For blockchain it must be deterministic, fast to compute, pre-image resistant (you cannot find the input from the hash), second pre-image resistant, and collision resistant (finding two inputs with the same hash is infeasible). It should also show the avalanche effect, where a one-bit change gives a completely different hash. Blocks, addresses, Merkle trees and proof of work all depend on these properties.
27
A product team wants to store user documents and personal details directly on a public chain. What do you advise?
Do not put personal data on a public chain. Data there is permanent, public and replicated globally, which conflicts with the right to erasure under India's DPDP Act and GDPR, and storage is extremely expensive. Store documents encrypted in off-chain storage, keep only a salted hash or commitment on-chain for integrity, and control access through the application. If the data must be deleted, delete the off-chain copy and the encryption key; the hash alone reveals nothing.
28
What is the difference between an execution client and a consensus client, and why does client diversity matter?
Since the Merge, an Ethereum node runs two pieces of software. The execution client, such as Geth, Nethermind, Besu, Erigon or Reth, runs the EVM, holds state and handles transactions. The consensus client, such as Lighthouse, Prysm, Teku, Nimbus or Lodestar, runs Proof of Stake. They talk over the Engine API. Client diversity matters because a bug in a client used by over two-thirds of validators could finalise an invalid chain and cause mass slashing.
29
What are the basic Foundry commands to create, build, test and work with a project?
curl -L https://foundry.paradigm.xyz | bash && foundryup
forge init my-dapp # new project with src, test, script
forge install OpenZeppelin/openzeppelin-contracts
forge build # compile
forge test -vvv # run tests with traces
forge coverage # coverage report
forge snapshot # gas snapshot
anvil # local node
cast call ADDR 'count()(uint256)' --rpc-url $RPC
Foundry tests are written in Solidity and run fast; Hardhat is the JavaScript or TypeScript alternative with a large plugin ecosystem.
30
How do you run Slither on a Foundry project and focus on important findings?
Install it with pip and run it from the project root; it detects Foundry automatically.
pip install slither-analyzer
slither .
# Only medium and high impact issues
slither . --exclude-low --exclude-informational
# Exclude dependencies
slither . --filter-paths 'lib|test'
# Print a summary of contracts and functions
slither . --print human-summary
Triage each finding: fix real bugs and record why false positives are safe.
Tips to crack the JP Morgan Chase Blockchain interview
Practise recorded video interview answers, keeping responses structured and within time limits.
Learn banking basics like payments, loans, KYC and risk controls for domain questions in technology and analytics roles.
Look up the Code for Good hackathon and JPMorgan's technology programmes if you are applying as a student or fresher.
Keep a one-minute story ready for every project on your CV: problem, your part, tools, result.
Practise the hard questions on this page aloud; JP Morgan Chase interviewers usually ask follow-ups on your first answer.
Frequently asked questions
How many rounds are there in the JP Morgan Chase Blockchain interview?
Candidates usually go through 5 stages: Online assessment (coding + aptitude); Video interview (HireVue style); Technical round; Hiring manager round; HR round. The exact rounds change with the role, team, location and your experience, so confirm the process with the recruiter.
Which topics should I prepare for the JP Morgan Chase Blockchain interview?
This practice set leans on dApp Development (6), Cryptography for Blockchain (6), Blockchain Fundamentals (5), Consensus and Scaling (4). Revise those first, then practise explaining one or two of your own projects end to end, because most JP Morgan Chase interviewers ask you to walk through real work.
Are these the exact questions asked at JP Morgan Chase?
No. These are curated practice questions that match the skills and difficulty usually tested in banking & finance interviews like JP Morgan Chase's. They are not a leaked or verified list of past questions.
Where does JP Morgan Chase hire Blockchain professionals in India?
JP Morgan Chase has large teams in Mumbai, Bengaluru, Hyderabad. Openings and locations change often, so check the JP Morgan Chase careers page and filter by city and experience.