Tech hiring Software engineering
Hire blockchain developers who test before they deploy.
A blockchain developer writes the smart contracts that hold and move value on a public chain, and the application code that talks to them. Deployed contracts are public, difficult to change and attacked from the first block, so we shortlist for testing discipline and security habits before anything else.
01 The role
What blockchain developers do all week, and what comes out of it.
A blockchain developer designs and writes smart contracts: programs deployed to a chain such as Ethereum, one of its layer-2 networks or Solana, which hold assets and enforce rules without an operator in the middle. They also build what surrounds the contracts: deployment scripts, indexers that turn on-chain events into queryable data, and the wallet-connected front end.
What makes the work hard is that mistakes are public and usually permanent. Anyone can read the bytecode, anyone can call any external function, and a transaction cannot be reversed. Reentrancy, a missing access check, a price oracle that can be manipulated inside one transaction or a rounding error in share accounting have each cost real projects their funds. The job is adversarial thinking, backed by fuzz and invariant tests.
Day to day, most work is on EVM chains in Solidity with Foundry or Hardhat, built on audited OpenZeppelin libraries rather than hand-rolled token code, and increasingly deployed to layer-2 networks. Solana work is a separate skill set in Rust, with a different account model. The role is also not the same as building a chain: protocol and node engineering is a rarer specialism.
What they ship
- Token contracts: ERC-20, ERC-721 and ERC-1155, with vesting and access roles
- DeFi contracts: vaults, staking, lending markets and automated market makers
- Upgradeable contract systems behind proxies, with timelocks and multisig admin
- Test suites: unit, fuzz, invariant and mainnet-fork tests
- Deployment and verification scripts for several networks
- Indexers and subgraphs that make on-chain events queryable
- Wallet-connected front ends and smart-account (ERC-4337) flows
02 Skills and stack
What blockchain developers work with, and what is optional.
Chains are not interchangeable. An excellent Solidity engineer is a beginner on Solana, and the reverse is equally true, so name your chain and language in the brief.
Core
The role cannot be done without these.
- Solidity and the EVM: storage, gas, calls, events
- Contract security: reentrancy, access control, oracle risk
- Testing: unit, fuzz, invariant and fork tests
- Token and vault standards (ERC-20, ERC-721, ERC-4626)
- Upgrade patterns, proxies and storage layout
- Transaction lifecycle, signatures and key handling
- Reading and reasoning about other people’s contracts
Tooling
Varies from team to team.
- Foundry (Forge, Anvil, Cast) or Hardhat
- OpenZeppelin Contracts
- viem and wagmi, or ethers.js
- Slither, Echidna or Medusa for analysis and fuzzing
- Ethereum and its layer 2s: Arbitrum, Base, OP Mainnet, Polygon
- Rust with Anchor for Solana programs
- The Graph or Ponder for indexing
- Chainlink or Pyth oracles
- Safe multisig and timelock controllers
- Tenderly and block explorers for tracing transactions
Adjacent
Useful, not required.
- TypeScript and React for the application front end
- Node.js services: relayers, keepers and indexing back ends
- Applied cryptography: signatures, Merkle proofs, zero-knowledge basics
- Gas optimisation and low-level Yul
- Tokenomics and mechanism design
- Move (Sui, Aptos), Vyper or Cairo
03 When to hire one
Signs you need a blockchain developer, and signs you need someone else.
The wrong hire for the problem is an expensive way to learn what the problem was. Check your situation against both columns.
Hire a blockchain developer when
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Your product’s core logic has to live on a chain
Custody, settlement or ownership must be verifiable by people who do not trust you. That is the case where a contract earns its complexity.
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Contracts are written and an audit is booked
Auditors find more when the code arrives with thorough tests and clear invariants. Someone has to prepare for the audit, answer findings and fix them properly.
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A contractor deployed the contracts and moved on
Nobody in the company can say what the admin keys control or how an upgrade would work. You need an owner before the first incident, not after it.
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You are moving to a layer 2 or adding a second chain
Bridging, differing gas models and cross-chain messaging bring their own failure modes. Experience on the target network saves expensive surprises.
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Web developers are learning Solidity on your mainnet code
Solidity looks like JavaScript and behaves nothing like it. Contracts that will hold customer funds should be written by someone who has done it before.
Look elsewhere when
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A database with an audit log would meet the requirement
If one organisation controls the data and users already trust it, a chain adds cost and risk for no benefit. An ordinary backend is cheaper, faster and easier to change.
Hire Node.js developers -
You only need to accept crypto payments or show wallet balances
That is integration with an existing provider’s API or SDK, not contract development. A capable full-stack developer can do it.
Hire full-stack developers -
The contracts are done and the work left is the web app
Wallet connection and transaction states are learnable. A strong React developer, with the contract author on hand to answer questions, will build a better interface.
Hire React developers -
You want an independent security audit
Whoever wrote the contracts should not be the one to sign them off. Use a specialist audit firm or a public contest; a security engineer can cover the infrastructure and key management around the contracts.
Hire security engineers -
There is no engineering team and you are launching a protocol
A launch needs contracts, front end, indexing, infrastructure and testing together. A single blockchain hire cannot review their own work.
See dedicated teams
04 How we assess
Four checks, before a name reaches you.
Every name on your shortlist has been through the same four stages. The notes and scores come with it.
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Stage 1
Profile review
We read deployed, verified contracts and public repositories: what the candidate wrote themselves, whether tests go beyond the happy path, whether the code was audited and how findings were handled. Hackathon projects count for less than contracts that held real value.
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Stage 2
Technical test
A timed test covering language and EVM fundamentals, common vulnerability classes and a coding exercise, such as writing a small contract with its tests or finding the flaw in one we supply.
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Stage 3
Conversation with our team
Our engineers ask the candidate to walk through a contract system they shipped: what its invariants were, who held the admin keys, how upgrades worked and what the audit found. We listen for how they think about an attacker.
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Stage 4
Review and levelling
Reviewers score accuracy, speed, problem-solving, communication and teamwork, then assign a level from our engineering framework. The notes say which chains and languages the person has used in production and which they have only studied.
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Then
Your shortlist
Assessed candidates, with notes and scores.
The engine
Evalia
Assessments run on Evalia, the assessment platform we built ourselves. Across the ProDevs network, more than 100,000 assessments have been completed.
The levels we assign are public. Read the engineering framework, or see how a hire runs from brief to offer.
05 Seniority
Three levels. What each one can own.
The title on a CV tells you little. What matters is how much a blockchain developer can be handed without someone checking each step.
Junior
Owns tests, scripts and integration
- Writes unit and fuzz tests for contracts designed by someone more senior
- Builds deployment scripts and front-end contract calls from an agreed interface
- Knows the common vulnerability classes and can spot them in simple code
- Should not be the only reviewer of anything that will hold funds
Mid-level
Owns a contract, design to mainnet
- Designs and writes a contract against a specification, with invariant tests
- Integrates safely with external protocols, tokens and price oracles
- Prepares code and documentation for audit and resolves the findings
- Runs testnet and mainnet deployments, including verification
Senior
Owns the protocol and its risk
- Designs the contract architecture, upgrade path and admin key arrangements
- Models economic and oracle attacks, not only bugs in the code
- Decides what goes on chain and what stays off it, and can cost both
- Leads incident response: pausing, communicating and recovering funds where possible
06 Interview questions
Interviewing a blockchain developer? Ask these.
For your own interviews, after ours. Each question comes with what a strong answer tends to show.
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Explain reentrancy. How do you prevent it, and where can it still catch you out?
A good answer shows: Checks-effects-interactions and reentrancy guards, then the harder cases: cross-function and cross-contract reentrancy, read-only reentrancy through a view function, and token callbacks. Someone who stops at “use a guard” has learned the slogan only.
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What invariants did your last contract have, and how did you test them?
A good answer shows: Statements that must always hold, such as total shares matching total assets, expressed as invariant or fuzz tests that run thousands of random call sequences. If the answer is only unit tests with fixed inputs, the edge cases were never explored.
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Your contract needs a token price. Where do you get it, and how could that be attacked?
A good answer shows: They distinguish a spot price from a pool, which can be moved within one transaction using a flash loan, from an oracle feed or time-weighted average. They also mention stale data and what the contract does when the feed stops.
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How would you make this contract upgradeable, and would you?
A good answer shows: Knowledge of proxy patterns, storage layout collisions and initialisers, plus the judgement that upgradeability is itself a risk: whoever holds the upgrade key can change the rules. Good answers involve a multisig and a timelock, or a case for immutability.
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Walk me through what happens between a user clicking “confirm” and the transaction being final.
A good answer shows: Signing in the wallet, the mempool or sequencer, inclusion, possible reordering by block builders, confirmations and finality, which differs between layer 1 and layer 2. They should know how the front end handles a pending, replaced or reverted transaction.
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Tell me about an audit finding on your own code. What did you change?
A good answer shows: A specific finding, its severity and the fix, with no defensiveness. The strongest candidates explain what they altered in their own process so that class of issue would be caught by tests next time.
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Which parts of this product should not be on chain?
A good answer shows: Anything private, large, frequently changing or without a trust requirement. A candidate who wants everything on chain will give you an expensive, slow product; one who can draw the line has built something real.
07 Ways to engage
Permanent, team, payroll or project. Four routes to a blockchain developer.
Most companies come to us for a permanent hire. If the work is temporary, or you cannot employ in the country, another model may fit better.
- Placement fee, of first-year salary. One-time.
- 10–15%
- Replacement guarantee on direct hires.
- 2 weeks
- To a first shortlist, for most roles.
- 48h
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Direct hire
A permanent employee on your contract and your payroll. One-time placement fee of 10–15% of first-year salary.
Tech hiring -
Dedicated team
A blockchain developer inside a team we assemble and run for you: product, design and engineering on your roadmap, for a monthly retainer.
Dedicated teams -
Outsourcing & payroll
A full-time person in a country where you have no legal entity. ProDevs employs and pays them: 20% of salary if we find the person for you, or 5% of salary, capped at $500 a month, for payroll and compliance on someone you have already chosen.
Outsourcing -
Freelance project
A defined piece of work with a clear end. You pay the agreed price per milestone through escrow, plus a 5% client fee. Free to post.
Freelancers
08 Around the role
Who blockchain developers depend on, and who depends on them.
A blockchain developer usually works in a small protocol team where every contract change is reviewed by at least one other engineer and then by outside auditors. In a company adding on-chain features to an existing product, they sit with the backend team and own the boundary between the two worlds.
- Front-end developer
- Supplies contract interfaces, events and error types, and explains what each transaction state means for the user.
- External auditors
- Hands over documented, tested code, answers questions during the review and fixes findings without introducing new ones.
- Backend developer
- Agrees which data is indexed off chain, how relayers and keepers are run, and where private keys are stored.
- Security engineer
- Plans monitoring, key management, pause procedures and the response if funds are at risk.
- Product and legal
- Translates token mechanics and regulatory limits into rules a contract can enforce.
09 Client testimonials
Hear it first-hand, from companies that hired.
Founders, operators and executives describe working with ProDevs, in their own words.
Play video: Client testimonial: Olufemi Seyi, COO, Casafina development company
Play video: Client testimonial: Aproko Doctor, Building AwaDoc
Play video: Client testimonial: JT Liddell, Promenade CEO
10 Questions
Before you hire a blockchain developer: the usual questions.
Something else? Book a call (opens in a new tab) and ask us directly.
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Which chains and languages do blockchain developers work with?
Most commercial work is on Ethereum and EVM-compatible networks such as Arbitrum, Base, OP Mainnet, Polygon and BNB Chain, written in Solidity. Solana is the main alternative and uses Rust. Sui and Aptos use Move. These are separate skill sets, so tell us the chain and language you have chosen and we shortlist against that.
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Do we still need an audit if we hire a senior blockchain developer?
Yes. A senior developer reduces the number of issues an audit finds and makes the audit cheaper and faster, but nobody reviews their own code reliably. Any contract that will hold customer funds should have independent review before mainnet, and again after significant changes. Budget for it from the start.
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Can a web developer learn Solidity on the job?
They can learn the syntax in weeks. The security mindset takes longer, because the failure modes have no equivalent in web development: public state, irreversible transactions, and attackers who profit directly from a bug. A web developer can grow into the role under an experienced reviewer, but should not write unsupervised code that holds funds.
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What is the difference between a blockchain developer and a Web3 front-end developer?
A blockchain developer writes the contracts and is accountable for their safety. A Web3 front-end developer builds the interface that connects a wallet, reads chain data and submits transactions, typically in React with viem and wagmi. Small teams combine the two; once contracts hold meaningful value, most separate them.
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How do you assess blockchain developers?
In four stages. We review contracts and repositories the candidate has shipped, set a timed technical test, hold a conversation with our engineering team about a system they deployed, then review the results together and assign an engineering level. The assessments run on Evalia. Our assessment is not a security audit of their past work.
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How quickly can we hire a blockchain developer?
For most roles you see a first shortlist within 48 hours of agreeing the brief, and most companies find their hire within two to three weeks. Your own interview process and the candidate’s notice period decide the rest. If the brief is specialised, such as a particular chain or zero-knowledge experience, say which requirements are fixed and which are preferences.
Talk to ProDevs
Tell us about the role.
Tell us the level and the stack. We will tell you how quickly we can put assessed blockchain developers in front of you.
Project work
Need it for a project instead?
Not every job needs a full-time hire. Describe the work, get proposals from vetted freelance blockchain developers, and pay per milestone through escrow. Free to post.