Sebastian Buza, Full-stack Developer in London, United Kingdom
Sebastian Buza

Full-stack Developer in London, United Kingdom

Member since November 23, 2017
Sebastian's helped companies from all around the world transform ideas into useful pieces of software that are used by millions daily. Recently, he's improved the core back end of Procore's payment system using his top-notch Ruby skills. Before joining Toptal, he served as the CTO at GGCrypto (a gaming platform) and Skupos as a lead software engineer. Sebastian knows that the key to successful remote work is exemplary communication.
Sebastian is now available for hire


  • Torstar
    JavaScript, React, Ruby on Rails (RoR), Ruby
  • Teespring
    JavaScript, Ruby on Rails (RoR), Ruby, React
  • Procore
    Ruby on Rails (RoR), Ruby



London, United Kingdom



Preferred Environment

GitHub, Git, RubyMine, Linux

The most amazing...

...piece of software I've ever built is a media server built with Crystal and Ruby for uploading images and videos with support for streaming.


  • Lead Full-stack Developer

    2019 - 2020
    • Integrated the newest React Create app with a Rails 4 app.
    • Used React Router, Redux, Thunk, and hooks.
    • Developed React components using Material-UI design.
    • Helped the team make a smooth transition from a full Rails-and-jQuery app to an app based on Rails, API, and React.
    • Updated key gems on the Rails app.
    • Set up and deployed the whole app to new staging environment.
    • Added Docker and Docker Compose to the development environment.
    Technologies: JavaScript, React, Ruby on Rails (RoR), Ruby
  • Full-stack Developer

    2019 - 2019
    • Developed the overall custom collections system for the Teespring app.
    • Built a full REST API on the back end to support basic operations such as CRUD and more complex such as export and import in bulk.
    • Added some missing indexes to the db and fixed some bugs related to controller helpers.
    • Built the front-end part using React with hooks.
    • Fixed bugs related to session flickering on the frontend Redux store.
    • Integrated Webpacker with the Rails 4 app.
    Technologies: JavaScript, Ruby on Rails (RoR), Ruby, React
  • Back-end Developer

    2019 - 2019
    • Implemented improvements which lessened the effects of database deadlocks.
    • Sped up the response time of the API.
    • Fixed a major problem in the system (NIL-related issue).
    • Helped the team migrate to API versioning.
    • Upgraded the overall payment services.
    Technologies: Ruby on Rails (RoR), Ruby
  • Lead Full-stack Rails and React Developer

    2018 - 2019
    BitLab BVBA
    • Constructed an API using Rails and GraphQL.
    • Built front-end components based on the ANT design.
    • Integrated Redux along side React Router and hooks.
    • Coordinated the whole back-end team's work flow.
    • Composed the GraphQL code via the use of metaprogramming and requiring very little boilerplate code; I also developed the library.
    • Implemented the automatic generation of documentation for GraphQL endpoints.
    • Organized the team using Atlassian board.
    Technologies: GraphQL, Ruby on Rails (RoR), Ruby
  • Full-stack Developer

    2018 - 2019
    Ourea Systems
    • Created a user-managed integration testing framework using RSpec and Active Admin.
    • Improved numerous sub services which used Ruby.
    • Optimized the developer workflow with Docker, Heroku, and CircleCI.
    • Improved the front-end features using Ember.js.
    • Generated PDF reports from HTML using wkhtmltopdf command line tool.
    • Tracked the statuses of background jobs.
    Technologies: Ember.js, Ruby on Rails (RoR), Ruby
  • Front-end Developer | Back-end Developer | DevOps

    2018 - 2018
    Freelance Work
    • Fixed numerous bugs and added features to projects which have been using Ruby on Rails.
    • Upgrade and migrate React apps to newer versions.
    • Enhanced the developer workspace using Rake, Git, Docker, and Docker-compose.
    • Helped teams move to React hooks.
    • Deployed a Rails apps to AWS, DigitalOcean, or VPS.
    • Configured Nginx servers and Cloudflare.
    • Stored images and documents with Rails 5 active storage.
    • Upgraded multiple apps from Rails 3/4 to 5.
    • Migrated Ember.js apps to newer versions.
    • Upgraded the deployment using Capistrano, Rake, Hatchbox, and Git.
    • Improved the appspeed when using PostgreSQL, MongoDB, Redis, and Elasticsearch by using more efficient queries, more performant gems, and an improved configuration of database systems.
    Technologies: Elasticsearch, Redis, Capistrano, Ember.js, React, Ruby on Rails (RoR), Ruby
  • Senior Ruby on Rails Engineer

    2018 - 2018
    • Started the project using Ruby on Rails.
    • Built a reliable API to handle front-end requests.
    • Constructed the database schema.
    • Documented the API using Swagger, Postman, and Apipie Gem.
    • Generated reports and documentation from RSpec testing.
    Technologies: Ruby on Rails (RoR), Ruby
  • CTO

    2017 - 2017
    • Setup the base for a React and Node.js application which connects to Firebase.
    • Configured a developer work environment with Docker and AWS Cloud9 Amazon Web Services.
    • Scaled Node.js code across multiple servers on AWS.
    • Developed a custom Redis-based system for matching up players.
    • Created reusable components in React.
    • Integrated Node.js with an Ethereum wallet.
    • Created the GGCrypto currency and managed it in the system.
    • Organized meetings for developers (standup, retrospective).
    • Managed and reviewed pull requests.
    • Architected the system for the future integration with Steam.
    • Managed Steam users and integrated the Steam chat into our app.
    Technologies: React, JavaScript, Firebase, Node.js
  • Lead Software Engineer

    2016 - 2017
    • Setup the Rails app, database, and Nginx server; then deployed them to AWS.
    • Developed the back-end API using JSON API resources.
    • Secured the back end with CanCanCan and tracked changes with a custom-built and private gem.
    • Created Rake tasks to import sample data for developers to use during development.
    • Implemented authentication, invitations, and Google Analytics.
    • Integrated a single-page app theme bought from ThemeForest.
    • Created front-end services to fetch CRSF tokens and monitor user online statuses.
    • Built background jobs to sync the database with a convenience store's (c-store) inventory.
    • Developed an electronic app for convenience stores to install (it was used for inventory syncing).
    • Created custom services to implement Ajax queries to the back end (Ember.js services and jQuery).
    • Enabled the app to cache the models using Web SQL Database.
    • Implemented a React-based login, registration, and blog.
    Technologies: Java, JavaScript, Ember.js, Ruby on Rails (RoR), Ruby
  • Full-stack Software Engineer

    2014 - 2016
    • Designed the API and implemented it using a JSONAPI-resources gem for the Ember.js front end.
    • Secured the operations on the back-end side using Pundit and Papertrail which tracks model changes.
    • Participated and taught others in a coding session; specifically on how to structure their code and be very productive with TDD.
    • Fixed the existing test suite which we had inherited from the previous developers.
    • Migrated the above existing test suite from MiniTest to RSpec.
    • Added background jobs through Sidekiq for operations which took longer than necessary.
    • Instigated a workflow change: we now deploy our code through Capistrano and configure the servers with Chef.
    • Converted the front end from being Backbone.js based to Ember.js—improving our productivity.
    • Developed a custom calendar component for holiday schedule; it used Moment.js for computing time ranges.
    • Used i18n everywhere to prepare for external use outside of Germany.
    Technologies: Ember.js, JavaScript, Ruby on Rails (RoR), Ruby


  • GGCrypto (Development)

    GGCrypto is a gaming platform built on top of Node.js, React, and Firebase. Its primary purpose is to have a cryptocurrency available for online games using the Ethereum blockchain. The currency is meant to be used for bets on matches and trading for in-game items.

    I've worked as the CTO along with some friends from Hong Kong and Romania. I set up the initial project, onboarded developers, and had the app up and running on using Docker and VPS. I also scheduled development meetings and helped recruit others to join the project.

    While working in a two-person team, my full-stack skills (front-end, back-end, DevOps) came in handy to successfully build the MVP in a month's time; soon after, we brought in more developers.

  • Skupos (Development)

    The Skupos platforms allow convenience stores and distributors to communicate with each other, create orders, and manage their inventories,

    Skupos, Inc. is their current name, but before it was Harbor Bay Supply. It first started as a warehouse for all types of goods. They needed someone to build an online store for convenience stores to order products from them.

    I built the web store using Spree and Rails. Then the CEO wanted to make a software version for more general use. To get the funds, Skupos had a fundraising event in which we raised $2.4 million with our demo app. (More information can be found at the link:

    In two months (320 hours), I built the demo app by myself, and with this MVP, the CEO approached venture capitalists and successfully raised $2.4 million. Afterward, we recruited more developers in the US, and I served on the project as the lead software engineer.

    For this project, I also created custom components and mixins to handle pagination, side loading, searching, image async loading, and more.

    Workflow: GitHub, CircleCI, AWS, Chef, Docker (The workspaces are in a browser using and other custom Rake tasks.)

  • Crewmeister (Development)

    ATOSS is an IT company which focuses on managing workforces through software. Their main app—ATOSS Staff Efficiency Suite—is designed for companies like BMW, Audi, and so on; at the time, they did not target smaller companies.

    The project that I've worked on for them was Crewmeister which targeted that specific market (smaller companies). For them, I used my skills in Ruby and Ember.js (which I learned by myself when I tried to build a gaming platform).

    On the back-end side, we used Rails, Nginx, and MySQL. We implemented the automation of payments using Stripe, regular email updates, and background jobs to processes Excel data from our customers.

    On the front-end side, we first used Backbone.js, but later we converted it to Ember.js to improve our productivity.

    Over time, I started making the final decisions regarding the architecture, libraries used, coding standards, and test suite.


  • Languages

    JavaScript, JRuby, Ruby, GraphQL, CSS, Java 8, SQL, HTML, SCSS, HTML5, Java, Elixir
  • Frameworks

    Ruby on Rails 5, Ember.js, Ruby on Rails (RoR), Svelte, Stimulus, Redux, Mocha.js, Sinatra, JavaScript MVC, Cuba, Material-UI, Materialize CSS, Phoenix
  • Libraries/APIs

    React, Ember FastBoot, Sidekiq, React Router, Antd, Lodash, jQuery UI, Rack, Ruby on Rails API, Node.js, Ember Data, jQuery, Socket.IO, FFmpeg, ImageMagick, Vue.js
  • Tools

    RubyMine, JavaScript Testing, Rake, Capistrano, RSpec, Redux Thunk, Chef, Git, GitHub, Gimp, Nginx
  • Platforms

    Linux, Windows, Firebase
  • Storage

    Cloud Firestore, PostgreSQL, Redis, MongoDB, Elasticsearch, JSON-LD, JSON, MySQL, Spring Data Elasticsearch
  • Other

    Full-stack, Google Cloud Functions, Organic SEO, Ember CLI, WebSockets, SEO Tools, Optimization, Axios
  • Paradigms

    Object-relational Mapping (ORM), Actor Programming, Pair Programming, Concurrent Programming


  • Master's degree in Software Engineering
    2016 - 2018
    West University of Timișoara - Timișoara, Romania
  • Bachelor's degree in Computer Science
    2013 - 2016
    West University of Timișoara - Timișoara, Romania

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