Radek Ostrowski, Ethereum Developer in Brisbane City, Queensland, Australia
Radek Ostrowski

Ethereum Developer in Brisbane City, Queensland, Australia

Member since September 24, 2014
Radek is a certified Toptal blockchain engineer particularly interested in Ethereum and smart contracts. In the fiat world, he is experienced in big data and machine learning projects. He is a triple winner in two different international IBM Apache Spark competitions, co-creator of PlayStation 4's back end, a successful hackathon competitor, and speaker at conferences in Australia, Poland, and Serbia.
Radek is now available for hire




Brisbane City, Queensland, Australia



Preferred Environment

GitHub, MacOS, Unix

The most amazing...

...achievement I've had is winning two international Apache Spark competitions run by IBM.


  • Blockchain Consultant

    2018 - PRESENT
    • Engaged with clients wanting to enter the blockchain space, especially in the Ethereum ecosystem.
    • Won a prize for my "Time Locked Wallet" demo project in ConsenSys, a uPort Blockchain and Identity hackathon.
    • Designed and deployed smart contracts for tokens and ICOs including token vesting, refund vaults, and multi-signature wallets.
    • Performed smart contract security audits.
    Technologies: Smart Contracts, Ethereum, Blockchain
  • Ethereum Engineer

    2020 - 2020
    British Asset – Kauri Crypto (via Toptal)
    • Created and deployed a staking contract for the platform token.
    • Created a demo DApp for the staking contract.
    • Implemented and deployed the graph for the staking contract tracking all events and allowing more advanced queries.
    Technologies: JavaScript, GRAPH, Truffle, Solidity, Ethereum
  • Ethereum Engineer

    2019 - 2020
    Zipmex Exchange (via Toptal)
    • Created an upgradable erc20 token contract using a call delegate proxy.
    • Deployed the project to mainnet, verified on Etherscan, and provided instructions to the team on how to use it.
    Technologies: Truffle, Solidity, Ethereum
  • Blockchain Engineer

    2019 - 2019
    LLPS, LLC (via Toptal)
    • Built a prototype of a real estate-backed loans platform.
    • Designed and built the Ethereum smart contracts forming the back end of the platform.
    • Created a user interface to the blockchain back end using React and Drizzle.
    Technologies: Drizzle, React, DApps, Web 3.0, Solidity, Ethereum
  • Blockchain Engineer

    2018 - 2018
    Grayblock (via Toptal)
    • Helped to design and build a POC platform leveraging blockchain to improve electricity generation finance.
    Technologies: DApps, Web 3.0, Solidity, Ethereum
  • Blockchain Engineer

    2018 - 2018
    IDEX – Aurora Labs S. A. (via Toptal)
    • Investigated various optimizations to Ethereum transaction throughput and gas cost for IDEX, currently the biggest on-chain exchange.
    • Prototyped several optimizations including scheduling and specialized smart contracts.
    Technologies: Node.js, Solidity, Ethereum
  • Solidity Expert

    2018 - 2018
    Coinuma SL (via Toptal)
    • Helped to integrate Ethereum into the cryptocurrency exchange being built.
    • Demonstrated wallet generation, ether and token transfers, balance checks, and listening for events.
    • Advised on best security practices.
    Technologies: Python, Web 3.0, Solidity, Ethereum
  • Blockchain Engineer

    2018 - 2018
    Fan Hero (via Toptal)
    • Provided consultancy on Ethereum.
    • Researched the use of permissioned blocks and IPFS.
    • Investigated transferring tokens without ether.
    • Prototyped a token contract.
    Technologies: IPFS, Solidity, Ethereum
  • Ethereum/Solidity Developer

    2018 - 2018
    Kryptonex LLC (via Toptal)
    • Helped to integrate Ethereum and ER20 tokens into an exchange that is currently being built. It included address generation, token listing, and basic wallet operation related to ether and tokens using Web3.js.
    Technologies: Web3.js, Ethereum, Solidity
  • Big Data Engineer

    2017 - 2018
    Commonwealth Bank of Australia
    • Provided consultancy on big data technologies and data science.
    • Architected and designed scalable solutions.
    • Developed solutions mainly with Apache Spark and Scala.
    • Employed machine learning techniques to maximize profit.
    • Led a team to victory in an internal hackathon—developed a Slack bot for knowledge discovery, deployed on AWS.
    Technologies: Machine Learning, Scala, Apache Spark
  • Big Data Engineer

    2016 - 2016
    Taulia, Inc. (via Toptal)
    • Designed and built a new generation of Taulia’s data analytics platform.
    • Effectively processed financial data and extracted useful information both in batch and real time.
    • Built the platform in Scala, Spark Streaming and SQL, Cassandra, Kafka, Docker, and Redshift, running on Kubernetes on AWS.
    Technologies: Amazon Web Services (AWS), Redshift, Kubernetes, Docker, Cassandra, Apache Kafka, Scala, Spark
  • Big Data Engineer

    2015 - 2016
    Method Mill
    • Helped integrate various data sources on a large scale.
    • Built a pipeline from MySQL to Amazon Redshift.
    • Created a syncing tool for Amazon S3.
    Technologies: Amazon Web Services (AWS), MySQL, Amazon S3 (AWS S3), Redis, Redshift, Docker, Akka, Scala, Spark
  • Big Data Engineer

    2015 - 2015
    Max2, Inc. (via Toptal)
    • Helped design and build a community-powered venue discovery platform offering personalized recommendations, planning with friends, and curated and real-time information.
    • Used SparkSQL with DataFrames for data ingestion and Spark Streaming and MLlib for analytics.
    • Coded in Scala with Akka and Kafka and run on Mesos.
    Technologies: Mesos, Akka, Apache Kafka, Scala, Spark
  • Senior Developer/Docker Evangelist

    2015 - 2015
    Tesco Bank
    • Introduced Docker to the development environment.
    • Helped improve the CI pipeline.
    • Extended the credit card portal.
    • Improved the user journey experience for a loan portal.
    Technologies: Docker, Git, Cucumber, Spring, Java
  • Big Data Engineer

    2015 - 2015
    Expedia, Inc.
    • Helped to automate the build and run process.
    • Prototyped with Apache Spark.
    • Updated existing Hive and MapReduce workflows.
    Technologies: Jenkins, Azkaban, Chef, Git, Apache Spark, Hadoop
  • Senior Software Developer/Team Leader

    2013 - 2015
    • Built a production RESTful Java web service for Sony devices and platforms mainly for Sony PS4 and 4K-TV handling hundreds of thousands of transactions.
    • Developed on top of Spring Framework and Cassandra.
    • Offered authentication and authorization capabilities based on OAuth2.
    • Focused on quality of the code by employing unit testing with 100% code coverage, BDD with Cucumber, code reviews with GitHub pull requests, and Jenkins.
    • Produced a project collecting, analyzing, and visualizing statistics from Sony devices. The data is stored in Amazon S3 and processed using Hadoop (MapReduce and Hive). The data collection server and the BI portals are Java based (Spring MVC and REST). I secured the access to the web services (by extending Spring Security) and the relational databases. Other technologies used include Apache Karaf (OSGi) and Maven.
    • Worked on the “One Account – All Sony” global unified accounts integration project for Playstation and other devices.
    • Led a team of three in Brussels and collaborated closely with the rest of the team in San Diego.
    Technologies: Splunk, GitHub, Jenkins, Amazon S3 (AWS S3), Amazon EC2, Apache Hive, Hadoop, OAuth 2, Cucumber, REST, Spring, Scala, Java
  • Senior Developer

    2012 - 2012
    DeltaDNA (GamesAnalytics)
    • Tackled the challenges of real-time data collection, predictive analytics, data measurement, and user engagement for the millions of online and mobile computer game sessions, personalizing the user’s gaming experience and increasing retention and revenue as a result through optimized game design and individually targeted in-game messaging.
    • Designed, developed, and provided continuous updates and enhancements of new features as part of an Agile in-house development team for the platforms and mobile SDKs.
    Technologies: Amazon Web Services (AWS), iOS, Android, Apache Hive, Hadoop, VoltDB, REST, Spring, Java
  • Applications Consultant

    2006 - 2012
    EPCC (University of Edinburgh)
    • Led “Work Package 3: Test, Delivery, and Support” from start to finish in an Excellent-rated, data-intensive research project for the EU.
    • Designed and implemented the test platform, new software components based on Java, REST, Spring, Hibernate, and HDFS and extended existing software components such as OGSA-DAI during the lifespan of the project.
    • Worked on a master of science in high-performance computing, “test infecting” the students by lecturing and leading tutorials on unit testing and extreme programming and Agile methods; also created and gave a lecture on cloud use cases.
    • Developed a RESTful presentation layer based on Jersey for the software program OGSA-DAI.
    • Designed and developed an iPhone application for the UK National Supercomputing Service.
    • Fixed performance problems involving CUDA, C, JNI, and Java code and improved its graphical user interface via a spinout company.
    • Contributed to the project investigating the usage of Hadoop/MapReduce and clouds (Amazon EC2/Eucalyptus) for the analysis of post-genomic data.
    • Enabled the integration of the UKQCD community with the International Lattice Data Grid by implementing a web service layer in Java.
    Technologies: Amazon Web Services (AWS), Hadoop, Spring, REST, Java


  • Topcoder/ConsenSys - uPort Blockchain and Identity Hackathon

    Designed and implemented Ethereum dApp, which won a prize in the hackathon. It consists of smart contracts and a web front-end, and can be used for time locking Ethereum and ERC20 tokens. The dApp could be used for crypto gifts and vesting.

  • My Perfect Weather - IBM Spark Competition

    I designed and built the web service that became a winner of the Grand Prize and the Fan Favourite award in the IBM Sparkathon.

  • Dipping into the Big Data River: Stream Analytics at Scale

    I presented my project at the biggest data conference in Australia. Recorded talk is available here:

  • Kaggle - Data Science Competitions

    My rankings demonstrate my ability to compete with the world's best data scientists:
    * Top 6% (100/1984) in Expedia Hotel Recommendation
    * Top 9% (84/979) in Outbrain Click Prediction

  • iWisps - IBM Spark Competition

    A fast, scalable, and portable local business recommender microservice powered by Apache Spark. I designed and built the project that became a winner in the IBM Spark competition and received a 'big check' at the IBM event in NYC.

  • Scala for Data Science

    I was a technical reviewer for the book.

  • Contributions to Spark Notebook

    Created a demonstration of anomaly detection in Spark using Spark SQL, Spark Streaming, and MLlib.

  • Contributions to Stubby4j

    Added functionality to serve files from the filesystem path based on the RegEx expression specified in the request.

  • Contributions to the Spring Security OAuth

    Extended the expression methods to allow testing for existing scope by specifying a RegEx expression.

  • The Ultimate ENS and ĐApp Tutorial (Publication)
    The Ethereum Name Service is a blockchain-backed alternative to the internet's traditional Domain Name System. If you own a .eth domain, you can deploy smart contracts that let users set up their own subdomains—but then, of course, you'll want a corresponding ĐApp to make it user-friendly. In this tutorial, Toptal Freelance Ethereum Developer Radek Ostrowski provides complete coverage of this scenario, this time with a focus on ĐApp development.
  • Time-locked Wallets: An Introduction to Ethereum Smart Contracts (Publication)
    Launch yourself into Ethereum smart contract development with the Truffle framework! In this tutorial, Toptal Freelance Ethereum Developer Radek Ostrowski shows you how to create a practical ĐApp in the Solidity language, complete with its own ERC20 token.
  • How I Used Apache Spark and Docker in a Hackathon to Build a Weather App (Publication)
    Hackathons often inspire engineers to create amazing software. By blending various technologies together, really useful and often fun projects can be realized in a short period of time. In this article, Toptal engineer Radek Ostrowski shares his experience participating in the IBM Sparkathon, and walks us through how he elegantly combined the power of Apache Spark and Docker in IBM Bluemix to build a weather app.
  • Getting Started With Docker: Simplifying DevOps (Publication)
    Docker, an open source tool, has changed the way we think about deploying applications to servers. By leveraging some amazing resource isolation features of the Linux kernel, Docker makes it possible to easily isolate server applications into containers, control resource allocation, and design simpler deployment pipelines. Moreover, Docker enables all of this without the additional overhead of full-fledged virtual machines.
  • Introduction to Apache Spark with Examples and Use Cases (Publication)
    In this post, Toptal engineer Radek Ostrowski introduces Apache Spark -- fast, easy-to-use, and flexible big data processing. Billed as offering "lightning fast cluster computing", the Spark technology stack incorporates a comprehensive set of capabilities, including SparkSQL, Spark Streaming, MLlib (for machine learning), and GraphX. Spark may very well be the "child prodigy of big data", rapidly gaining a dominant position in the complex world of big data processing.


  • Languages

    Solidity, Scala, Java, Python, JavaScript
  • Frameworks

    Truffle, Apache Spark, Play Framework, Spring, Hadoop, OAuth 2, Spark, Akka
  • Libraries/APIs

    Spark Streaming, Web3.js, Node.js, React, Drizzle
  • Tools

    Git, Spark SQL, Cucumber, Jenkins, GitHub, Splunk, Chef, Mesos
  • Paradigms

    Data Science, Agile Software Development, Functional Programming, Scrum, Kanban, REST
  • Platforms

    Android, Drupal, Blockchain, Ethereum, Docker, Linux, MacOS, Kubernetes, Hyperledger, R3 Corda, Apache Kafka, Amazon Web Services (AWS), Amazon EC2, iOS, Unix
  • Storage

    NoSQL, Cassandra, Redshift, Apache Hive, Amazon S3 (AWS S3), VoltDB, Azkaban, Redis, MySQL
  • Other

    Ethereum Smart Contracts, Machine Learning, Data Engineering, Freelance, Altcoin, Smart Contracts, IPFS, Web 3.0, DApps, GRAPH


  • Master of Science (with Distinction) Degree in High Performance Computing
    2005 - 2006
    University of Edinburgh - Edinburgh, UK
  • Bachelor of Science (with Honors) Degree in Computing
    2004 - 2005
    Edinburgh Napier University - Edinburgh, UK
  • Bachelor of Science Degree in Physics with IT
    2001 - 2004
    Nicolas Copernicus University - Torun, Poland


  • Architect Certification for Apache Cassandra
    JUNE 2017 - PRESENT
  • Developer Certification for Apache Spark
    MAY 2015 - PRESENT
  • Java Web Services Certified Expert

To view more profiles

Join Toptal
Share it with others