Radosław Szalski, Developer in Poznań, Poland
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Radosław Szalski

Verified Expert  in Engineering

Full-stack Developer

Poznań, Poland
Toptal Member Since
August 29, 2017

Radosław is a full-stack developer working in TypeScript, Go, and Python. He has 10+ years of professional experience engineering web applications, including at the architecture level. While working with many different technologies, he focuses on full-stack development, craftsmanship, and testing processes. Radosław enjoys automating DevOps tasks with Ansible and Terraform and writing tools that empower engineers to be 10xers. He is also experienced with recruiting and onboarding engineers.


Silo Technologies Inc.
JavaScript, React Native, ECMAScript (ES6), Redux, TypeScript, Go, DevOps, MobX...
Silo Technologies Inc.
JavaScript, React Native, ECMAScript (ES6), Redux, TypeScript
Hawkker (via Toptal)
Amazon Web Services (AWS), TypeScript, REST, Unit Testing, Pytest...




Preferred Environment

Chrome Developer Tools, Zsh, PyCharm, Git, Linux, MacOS, GoLand, WebStorm, iTerm2

The most amazing...

...project I've developed is an intuitive library that recursively parses XML documents into interactive Python objects and back.

Work Experience

Full-stack Developer

2020 - PRESENT
Silo Technologies Inc.
  • Started, spearheaded, and oversaw the implementation of a design system. Together with the introduced Storybook, it serves as a foundation for building components. It has delivered immense value and compound on increased developer productivity.
  • Improved the front-end release process, which affected all engineers. Advocated for the writing and maintaining of SOPs for the entire team.
  • Analyzed the risks to the company from an engineering standpoint and subsequently proposed a migration off of Heroku. Prepared engineering planning and analysis documents with plans for a stop-gap migration.
  • Worked constantly on tech debt and architectural improvements while also working on important product features. Also did work on observability on the front and back end and trained and coached employees.
  • Focused on empowering front-end engineers by bringing them the best tools, configuring the fastest environments and pipelines, and introducing state-of-the-art patterns after researching them. Addressed complex challenges no one else wanted to touch.
  • Introduced a dedicated business logic layer powered by MobX. It has become the standard for handling complex logic on the front end and something we simply never architected for before. It allowed the entire team to decouple business logic from UI handling.
  • Migrated the front end from Create React App to Vite and improved E2E development velocity by speeding up compilation times by more than 10x.
  • Introduced GraphQL to Silo, which involved designing schemas from scratch, configuring tooling and observability, and establishing a lot of patterns for data fetching and testing, and overall development.
  • Advocated for and migrated the old Wiki and most of the team's documents into a unified and easy-to-use tool, Notion.
Technologies: JavaScript, React Native, ECMAScript (ES6), Redux, TypeScript, Go, DevOps, MobX, PostgreSQL, Git, GitHub, Jenkins, Heroku, Terraform, Kubernetes, Graphite, Datadog, Cypress, Playwright

React Native Developer

2019 - 2020
Silo Technologies Inc.
  • Developed an entire mobile app for native Android and iOS from start to finish as a single engineer. Handled the entire lifecycle of the application, from implementing designs, through architecture to building tools and CI/CD pipelines.
  • Transitioned the entire company from JavaScript to TypeScript, which resulted in a massive maintainability boost and velocity increase. To this day, 100% of Silo is TypeScript-based.
  • Mentored the team and helped out in areas other than the mobile app (e.g., React web, back end, and more). Transitioned the team to a proper E2E testing framework, Cypress.
Technologies: JavaScript, React Native, ECMAScript (ES6), Redux, TypeScript

DevOps/Full-stack Engineer

2018 - 2020
Hawkker (via Toptal)
  • Used AWS CloudFormation templates (Infrastructure as Code) to provision multiple identical highly available AWS environments. Integrated Sentry and DataDog agents, enabling the monitoring of every environment and release process.
  • Maintained and extended a Django-based REST API and a React-based SPA. Migrated from Django v1.11 to v2.2 in a production-serving REST API.
  • Used Python to automate the deployment and release process of both back-end API and front-end SPA. Integrated with AWS CloudFormation for verification of parameters for each environment.
  • Introduced GitBook as a documentation hub and configured GitHub projects. Wrote extensive documentation on the release process of all the apps, security best practices, push notification configuration, and more.
  • Improved the ServiceWorker configuration and created a native Android app utilizing Trusted Web Activity to seamlessly utilize the PWA version of the website. Worked on the native iOS app to fix bugs and provide ongoing maintenance.
Technologies: Amazon Web Services (AWS), TypeScript, REST, Unit Testing, Pytest, Docker Compose, Flask-RESTful, React Navigation, Amazon Route 53, AWS CodePipeline, REST APIs, Python 3, GitFlow, Full-stack, iOS, Android, Progressive Web Applications (PWA), PWA, PostgreSQL, Django REST Framework, Django, React, JavaScript, Python


2016 - 2020
  • Screened, recruited, and coached Python, JavaScript, and Unity developers.
  • Performed extensive code reviews for the entire team and was a point of contact for any and all challenges they faced.
  • Orchestrated dozens of virtual servers and databases across multiple environments on AWS using Ansible, Terraform, and Packer.
  • Owned all architectural choices, from game architecture to back-end designs.
  • Created production-quality REST APIs in Python with authentication, logging, and metrics instrumentation (using Prometheus). Designed, implemented, and maintained back ends on AWS for various games and applications.
  • Performed load testing and benchmarking of every developed microservice using Locust.io, Ab, Apib, and Wrk.
  • Designed gorgeous metric dashboards using Grafana that allow every team member to see a high-level overview of the environments as well as dig into details if needed. Data sources included AWS CloudWatch, self-hosted Prometheus, and SQL connectors.
  • Benchmarked and tuned the whole application stack, from Linux Kernel parameters through NGINX/uWSGI configuration options to AWS design choices.
  • Consulted as the go-to guy for hard technical and business problems for the whole team. Negotiated with clients and analyzed requirements for upcoming games, services, and projects.
Technologies: Amazon Web Services (AWS), TypeScript, REST, Unit Testing, Pytest, Docker Compose, NGINX, Flask-RESTful, React Navigation, Amazon Elastic Container Service (Amazon ECS), Amazon Route 53, AWS CodePipeline, REST APIs, Python 3, GitFlow, Locust, AWS Lambda, GitHub, Django, Alembic, SQLAlchemy, Falcon, Flask, Grafana, Prometheus, Packer, Terraform, Ansible, React Native, React, Python

React Native Developer

2018 - 2019
MobileCoin (via Toptal)
  • Developed a cryptocurrency wallet app for iOS and Android in React Native, backed by both Firebase and a crypto ledger, with support for wallet generation, export and recovery, multiple currencies, QR code scanning and various security features.
  • Worked on compiling a multi-target toolchain using Android NDK for cross compilation of a Rust library that was a native dependency.
  • Introduced Flow for static type checking, linters and Redux, worked proactively on workload planning and the CI/CD pipeline.
  • Deployed a URL redirector for Deep Linking support using AWS Lambda and CloudFront.
  • Worked on integrating Rust-based cryptocurrency payments into a fork of the Signal Messenger app.
Technologies: Cryptocurrency, Unit Testing, Docker Compose, Redux-Saga, Amazon Route 53, GitFlow, Cryptography, Sketch, Zeplin, Firebase, Android, iOS, Objective-C, Swift, Bitrise, Flow, Redux, React, React Native

Senior Python Developer

2018 - 2018
Croscon (via Toptal)
  • Extended and fixed business-critical functionality for live customers.
  • Worked on asynchronous file import/export endpoints for high-volume bulk transfers.
  • Implemented new end-user workflows involving schema migrations.
  • Integrated a React web app with REST API.
  • Improved code coverage by writing functional and unit tests for new and existing code.
  • Introduced type hints to a Python 3.6-based project.
  • Migrated Peewee ORM from version 2.x to 3.x in an API with complex queries.
  • Worked with MySQL with custom DB-level encryption requiring key sharing through Celery tasks.
Technologies: Unit Testing, Pytest, Python 3, MySQL, peewee, SQLAlchemy, Celery, Docker, Marionette.js, Backbone.js, React, Flask, Python

Senior Full-stack/Python Engineer, Team Lead

2015 - 2017
STX Next
  • Managed multiple products in the whole project.
  • Decided on architecture for each application.
  • Analyzed client requirements and advised clients on technology choices.
  • Managed the whole software development cycle of multiple, cross-dependent production services.
  • Developed a branching strategy in Mercurial.
  • Reviewed code for every change made by every developer in my team.
  • Advocated and coached team members on pair programming and automated testing.
  • Owned and handled DevOps tasks, including orchestration and configuration management of environments and services using Ansible and Vagrant.
  • Ensured that complicated and intertwined stuff worked according to business rules.
  • Maintained multiple production applications, both legacy and greenfield.
  • Wrote documentation and tutorials for new developers.
  • Gave technical interviews and provided technical onboarding for many highly skilled employees.
  • Profiled and optimized performance of back-end Python code and front-end JavaScript.
  • Managed the whole team: trained and coached them, performed appraisals, and planned goals for upcoming months.
Technologies: Unit Testing, Pytest, NGINX, REST APIs, Python 3, GitFlow, Jira, CVS, Subversion (SVN), Mercurial, Pyramid, Git, Supervisord, Vagrant, Ansible, jQuery, JavaScript, Python

Senior Python Engineer

2014 - 2015
STX Next
  • Worked in Agile teams on multiple production services for the banking sector delivering immense business value.
  • Analyzed complicated requirements and planned work for Scrum sprints.
  • Managed and improved a legacy codebase while simultaneously delivering business value by developing new features.
  • Presented products to new and existing clients.
  • Advised clients on technology choices.
  • Managed a Jenkins CI server, BI dashboards, and multiple virtual servers.
  • Focused on quality, automating unit and integration tests.
  • Educated colleagues on proper testing, mocking techniques, and advanced VCS usage.
  • Continuously improved code testability and maintainability even in the legacy parts of the system.
Technologies: Unit Testing, Pytest, NGINX, REST APIs, Python 3, GitFlow, Fabric, Jenkins, Mercurial, Git, Pyramid, Ansible, jQuery, JavaScript, Python

Technical Referent

2013 - 2014
Poznan University of Technology
  • Ensured that researchers and students had working equipment and environments to work with.
  • Managed computer networks, CS lab equipment, and various on-premises hosted platforms (ticketing system, project management software).
  • Automated the provisioning of OSes in every lab using TFTP and PXE.
Technologies: Unit Testing, NGINX, Python 3, Linux, PXE, TFTP, Python

Software Engineer/Researcher

2012 - 2014
Poznan University of Technology
  • Developed a network testbed management framework in Python for scheduling experiments on wireless nodes.
  • Designed an experiment description language and parser allowing reproducible test runs on this framework.
  • Developed Linux kernel modules integrating with a Linux network stack and improving QoS scheduling.
  • Designed and implemented crawlers/scrapers for Twitter and Facebook (both API and front-pages) using Java.
  • Developed SIP clients integrating with a self-hosted Open IP multimedia subsystem.
  • Wrote academic papers and performed wireless network related research.
  • Designed experiment scenarios and user stories to be included in my papers.
  • Supervised work of students and interns.
Technologies: Unit Testing, NGINX, LaTeX, Python 3, GitFlow, UML, SIP, C, Java, Fabric, Python

Coinego | React Native Cryptocurrency Portfolio Manager

A React Native cryptocurrency portfolio manager where users can define their crypto portfolio to view its worth, observe selected coin prices, and get notified of changes.

I built Coinego from scratch using React, Redux, Redux-Saga, React Flow, and Jest and integrated it with REST API for coin prices. I also created a fully automated CI/CD pipeline with Bitrise and Fastlane, which automatically deploys to the Play Store.

React Native Demo Project

A To Do list manager written using React Native.

• Front-end created in React Native for iOS/Android enabling the management of tasks with support for attachments
• Access to Camera API (taking photos, media library)
* Access to Contacts API
• Access to Share API
• State management with Redux and Redux-Saga
• Back-end REST API created in Python using Django + Django REST Framework
• JWT token authentication
• Automated tests with Jest/Enzyme/PyTest
• Linting: eslint/pylint

Idle Car Factory | Mobile Game Back-end

Created the back-end architecture for a mobile game that has over 500,000 installs and receives hundreds of requests per second on Amazon Web Services. The architecture consists of a tier of web servers hosting a REST API written in Python (by me), load balancers, and PostgreSQL database. All of this managed using infrastructure as code where every resource is represented in Terraform and all of the servers are provisoned using Ansible. This allows for rapid deployment of multiple copies of whole environments and ensures that every change is versioned and documented.

Python SDK for the YOTI Platform (via Immergo)

Designed and implemented a Python SDK for the YOTI platform. Designed plugins for Flask and Django that used this SDK. Coordinated work of other Python programmers. Communicated with both business and programmers.
See: https://www.yoti.com/developers/documentation/?python

Mappet | XML To/From Python Mapper

This is a pure Python library developed to ease the pain of working with XML-based APIs and ESBs. It includes an elegant XML recursive parser based on lxml, which allows every XML document to be represented as a Python object. Such an object allows one to access XML nodes/attrs/children as object attributes, which makes it very intuitive to use. This library has a very high unit test coverage and has been open sourced thanks to my efforts while working in STX Next.

eRFC | RFC to Ebook Converter

This is a simple Python project exhibiting the Unix tool philosophy, "Do one thing well." It is the result of my frustration with the formatting of plain-text RFCs on Kindle. It is well documented and has a simple and elegant CLI interface (created with docopt library).

Jonnyguru.com | PSU Reviews Crawler

This is a Python crawler for power supply unit reviews on the fantastic and thorough Jonnyguru.com website. Written using the most popular crawling library in Python, Scrapy, it illustrates my approach to challenges: Automate it and share with the world.

Because having a good PSU for your PC is really important.

Master's Thesis

"Real-Time Bidding Supply-Side Platform Emulator" - Included a Python implementation of SSP emulator in the RTB ecosystem using big data bidding datasets.

Bachelor's Thesis

"Flow Utility Estimation and Signaling in Wireless Networks Managed by the DANUM System" - Describing work on flow shaping and QoS in wireless mesh networks using a custom kernel network stack.
2014 - 2016

Master of Science Degree in Computer Science

Poznan University of Technology - Poznań, Poland

2010 - 2014

Bachelor of Science Degree in Computer Science

Poznan University of Technology - Poznań, Poland


jQuery, REST APIs, React, MobX, React Navigation, Redux-Saga, Flask-RESTful, React Redux, Fabric, SQLAlchemy, Backbone.js, Marionette.js, peewee, Asyncio, Node.js, Pandas, Playwright


GitHub, Mercurial, Docker Compose, PDB, PyCharm, Vagrant, Pytest, Travis CI, Amazon Elastic Container Service (Amazon ECS), AWS CodeBuild, Grafana, Git, Terraform, Ansible, Packer, VirtualBox, NGINX, Flow, Zsh, Chrome Developer Tools, Supervisord, Subversion (SVN), CVS, Jira, Celery, Zeplin, Sketch, Jenkins, Sublime Text, LaTeX, Fastlane, GoLand, WebStorm


React Native, Swagger, Tailwind CSS, Cypress, Redux, Django REST Framework, Flask, Pyramid, Next.js, Alembic, Locust, Django, Jest


JavaScript, Python 3, Python, TypeScript, Falcon, HTML, HTML5, Go, GraphQL, Java, C, UML, Sass, SQL, CSS3, Bash, CSS, Swift, Objective-C, ECMAScript (ES6)


REST, Unit Testing, Clean Code, DevOps, Functional Programming, Extreme Programming, Microservices Architecture, Object-oriented Programming (OOP), DRY, Test-driven Development (TDD), Agile Software Development, Scrum, KISS, Kanban, Microservices, Web Architecture


Bitrise, Docker, AWS Lambda, Linode, Linux, Visual Studio Code (VS Code), Amazon Web Services (AWS), MacOS, Firebase, Android, iOS, Bluetooth Low Energy (LE), Heroku, Kubernetes


Amazon S3 (AWS S3), MySQL, PostgreSQL, Redis, SQLite, Datadog


Code Review, GitFlow, Full-stack, Web Development, Web Hosting, Startups, APIs, Software, Cloud Infrastructure, Full-stack Development, Front-end, Back-end, Mentorship, Google Play Store, App Store, AWS CodePipeline, Amazon Route 53, Prometheus, Architecture, Web Scraping, Software Architecture, SIP, TFTP, PXE, PWA, Google Material Design, Cryptocurrency, Cryptography, Progressive Web Applications (PWA), iTerm2, Advertising Technology (Adtech), API Documentation, Graphite

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