Konrad Gadzinowski, JavaScript Developer in Warsaw, Poland
Konrad Gadzinowski

JavaScript Developer in Warsaw, Poland

Member since May 23, 2017
Konrad is a highly skilled software developer who has delivered numerous web and mobile applications. He has created software for multiple small and larger companies, helping them to generate combined revenue of millions of dollars. He's a great team player and a proactive self-starter. He has the skills of a full-stack JavaScript developer, which enables him to see the whole picture and deliver projects faster and with higher quality.
Konrad is now available for hire




Warsaw, Poland



Preferred Environment

IntelliJ, Git, OS X or Ubuntu

The most amazing...

...thing I've created is an app that solves nesting and packing optimization problems in the furniture industry. It uses advanced machine learning techniques.


  • Full-stack JavaScript Developer

    2019 - PRESENT
    Large US-based Self-driving Car Company (via Toptal)
    • Developed web applications that use mostly map view.
    • Created complex UI interfaces using React.
    • Worked on integration with PostgreSQL database.
    • Wrote tests for both back and front end.
    • Helped develop web-based simulators and mapping applications.
    Technologies: JavaScript, TypeScript, PostgreSQL, Node.js, React
  • Full-stack Web Developer

    2017 - 2019
    Buho (Contract)
    • Developed a complete real estate web application.
    • Implemented an interactive map.
    • Added a grid of properties.
    • Enabled signup using Google and Facebook accounts.
    • Implemented a full-fledged CMS system that allows an administrator to completely customize the UI, in multiple languages.
    • Implemented automatic translation of pages to specific languages using Google Translate.
    • Added asynchronous loading of all elements.
    • Implemented an API interface to communicate with the mobile application.
    • Created a reusable set of elements that sped up further development.
    • Implemented Stripe payment system.
    Technologies: Node.js, TypeScript, SCSS, JavaScript, MongoDB, Gulp, Stripe
  • Freelance Full-stack Web Developer

    2017 - 2019
    Nextech (via Toptal)
    • Implemented two-factor authentication.
    • Added printing documents to PDF.
    • Created an administrator panel.
    • Improved security and general application architecture.
    • Introduced asynchronous loading of elements and pages.
    • Developed a document editor that allowed simultaneous work and saved ongoing changes in a history.
    • Implemented Stripe payment system.
    Technologies: JavaScript, PHP, Node.js, MySQL, Duo Security, Stripe
  • Freelance Front-end Developer

    2017 - 2017
    CivicLift (via Toptal)
    • Created multiple UI components using React.
    • Added multiple screens based on mockups.
    • Implemented user flow for multiple cases.
    • Improved database schema validation.
    • Helped reach a crucial deadline on project delivery.
    Technologies: JavaScript, React, Meteor, Stripe
  • Software Engineer

    2015 - 2017
    TomTom NV
    • Developed a map search engine back end using Java with Lucene library.
    • Developed an app proxy using JavaScript and Node.js.
    • Hosted an application on Amazon AWS cloud.
    • Hosted an application on Azure cloud.
    • Supported delivery of an application to major automotive companies.
    • Created extensive documentation about online search service on a developer portal.
    Technologies: Java, JavaScript, Node.js, AWS, Azure, Lucene, Git, Packer, Bash
  • UI Engineer

    2014 - 2015
    Massive Interactive Media, Ltd.
    • Created a UI layer for a video-on-demand application.
    • Added functionality to download movies to mobile devices to watch them later.
    • Deployed a mobile application to iOS and Android using a single codebase.
    • Added an option to easily customize a base application for future customers.
    • Adapted a base video-on-demand application for smart TV use.
    Technologies: JavaScript, Java, Objective-C, Haxe
  • Mobile App Developer – Contract in London, UK

    2014 - 2015
    Insane Logic, Ltd. (Contract)
    • Implemented a billing system in the mobile application.
    • Added flow for games.
    • Encrypted an embedded database.
    • Designed embedded database structure.
    • Gathered feedback from users regularly and improved the application towards the suggested direction.
    Technologies: Java, Android, SQLite
  • Independent Software Developer

    2012 - 2014
    Reptile Mobile
    • Created a collection of games for a marketing division of a large pharmaceutical company.
    • Delivered a point-and-click game in JavaScript for a marketing company.
    • Developed a music editor for Android.
    • Built an application that solves cutting and packing problems in the furniture industry using machine learning.
    • Created a nightstand clock and alarm for Android.
    • Delivered a skeuomorphic timer for iOS.
    • Built a task and calendar application for Android.
    • Built and sold the brightness battery widget for Android.
    • Developed a countdown widget for Android.
    • Created and sold a photo editor for Android.
    • Built and sold a BMI calculator for Android.
    • Delivered a flashlight application for Android.
    • Helped create a T9 keyboard for Android.
    • Created an application that detects hemoglobin level in blood based on the shade of a blood sample.
    • Delivered a bespoke productivity application for Android called To Do Timer.
    • Built a base mobile application and administrator web portal for an audio book company.
    • Created an action game about flying pigeons for iOS and Android using Unity framework and C#.
    • Delivered a news aggregator for Android.
    • Collaborated with multiple companies, large and small. Helped them to create great software and increased their combined revenue by millions of dollars.
    Technologies: JavaScript, Java, Objective-C, HTML, CSS, jQuery, Android, iOS
  • Automation Design Engineer

    2010 - 2012
    • Designed automatic production lines.
    • Helped create software for production automation machines.
    • Worked with multiple large production organizations.
    • Developed drivers for large industrial machines.
    • Supported and developed automatic production processes.
    Technologies: C, PLC Programming


  • Búho Home (Development)

    Búho Home is a web application for selling and renting real estate properties. As a user, you can view properties using a map and a grid. Payments support promo codes and are handled by Stripe. It’s possible to sign up using Google and Facebook accounts.

    It includes a fully-fledged CMS system for managing pages in multiple languages. It also has a built-in automatic translation using Google Translate.

  • TimeZonely (Development)

    See and compare multiple time zones at once. Never warp your brain with time zone math again.

    This application allows you to display numerous time zones. It delivers a customized experience through a slick interface so that you only see what you need to.

  • Mp3 Ringtone Factory (Development)

    Mp3 Ringtone Factory is an Android application used to edit MP3, WAV, AAC, and AMR audio music media files and create ringtones, alarms, and notifications from them. Using this app, you can also edit alarms, notifications, tunes, and ringtone audio media files in MP3 and other audio tune formats.

    - Play ringtones, alarms, and notifications and other audio media music tunes in MP3 and other audio tune formats
    - Trim and edit audio to ringtones, alarms, and notifications and other audio media music tunes in MP3 and other audio tune formats
    - Option to set ringtone loop number
    - Zoom options: Zoom in, out, show all
    - Different skin colors
    - Audio library with many sorting options

  • NestPack (Development)

    NestPack - A solution for nesting, cutting (optimization of number of sheets), and packing problems. This app is created to solve all optimization problems related to nesting, cutting, and packing. It's dedicated to the furniture industry, but also can be used with success in other industries, e.g., for logistics.

    The app contains two modules:
    - Nesting (cutting optimization): Helps you to reduce the number of sheets and prepare a final offer for your product.
    - Packing optimization: Help you to estimate the minimal number of trucks required to transport a given cargo. It's a very handy solution for almost every industry.

  • Tasks + Calendar Sync (Development)

    Tasks + Calendar Sync brings the full Google Tasks and Calendar experience to Android.

    Using this single app, you will be able to control your tasks and calendar from one point in your device. The app will synchronize across all your devices keeping your tasks and events in a consistent state where ever you are.

    The application was sold in April 2014 to Firstegroup, Ltd.

  • Final Alarm Xtreme (Development)

    Final Alarm Xtreme is a smarter Android alarm clock that is going to help you to wake up gently.

    Using your device accelerometer, it can record your sleep cycles and then try to wake you up gently during a light sleep cycle before the set alarm. The sleep data is saved and analyzed so that you can understand and improve your sleeping habits.

  • Final Countdown Widget (Development)

    A countdown timer widget to add some urgency, excitement, and order to a user's life. It counts down or counts up to a set event.

    It will help the user to manage their tasks. They will be able to see time and days left. The app enables the user to set a date by using a convenient calendar.

  • My Timer HD (Development)

    My Timer HD is a great tool giving you a feeling of real-world timers in your iOS device. You can interact with timers just like you do with real devices.

    This great productivity app enables you to:
    - Set as many timers as you want
    - Choose between 11 different app colors! Match the color of the app to you iPhone or a mood!
    - Use 12 unique, beautiful timers - including stopwatch, kitchen timers and many more!
    - Specify timer names, time to countdown, or date to count to
    - Choose if you want to see count down or up
    - Set snooze
    - Choose from thirteen different alarm sounds
    - Enable vibration during alarm

  • Task Timer + (Development)

    Task Timer Plus is a one of a kind Android productivity app. It's an agenda and to-do app, but with timers and graphs. You can easily see how your day is going to play out and when you'll have time to get stuff done.

  • Night Alarm Display (Development)

    Great night display for Android devices that shows clear hours and minutes; what's more, it keeps the screen on the whole time.

    It is a perfect replacement for traditional digital clocks. it's one of the most advanced alarm clocks on the market that show a digital clock on a screen.

  • Search Flashlight LED (Development)

    Flashlight app for Android devices. Incredibly simple and yet very useful flashlight application.

    - Use your device camera LED
    - Has screen as a torch with custom color
    - Widget for quick access

    This app was made as an add-on for Night Alarm Display application.

  • Bad Pigeons (Development)

    Flap the little wings of the pigeon in this addictive, thrilling, action packed flying adventure.

    Meet the city pigeon ready to poop on everything that he can! It's a simple, funny game where you can see the big world from the ground to the stars while playing the role of a city pigeon.

  • CBA News Reader (Development)

    CBA News Reader is a fast and powerful mobile news feed reader for your country’s major newspapers.

    It supports over thirty countries (e.g., USA, UK, Ireland, India, Canada, Australia, Malaysia).

    Choose, read, and easily search the most famous newspapers with your mobile device free of charge and in the fastest way possible.

  • T9 A Keyboard (Development)

    T9 keyboard was delivered for a London-based startup. The app offers different keyboard layouts including QWERTY and T9 layouts.

  • Quick Pic Editor (Development)

    Quick Pic Editor is an app designed for quick shooting, editing, and sharing photos.

    - Trimming photos
    - Resizing photos
    - Rotating photos
    - Adjust brightness, contrast, and saturation
    - Adjust sharpness and blur levels
    - Add pixelate effect
    - Change photo into meme
    - Add border
    - Different photo effects

    The application was sold in April 2014 to Firstegroup, Ltd.

  • Proper Weight & Body Fat (Development)

    An app created to help users to keep fit and to manage their weight.

    It is a BMI, WHtR, and body fat percentage calculator.

    Users can calculate their body mass index, waist-to-height ratio, and body fat percentage to find their ideal weight based on age and gender.

    The application was sold in April 2014 to Firstegroup, Ltd.

  • Brightness Battery Widget (Development)

    An Android app that auto-adjusts the screen brightness based on battery level. It contains a widget that indicates battery level and screen brightness.

    The application was sold in April 2014 to Firstegroup, Ltd.

  • Audiobook – Return To Marshalls Bayou (Development)

    An audiobook developed for Android devices using native technology.

    The mobile application cooperates with the back-end server that enabled an administrator to send messages about new audio books to all users, using Google Cloud Messaging technology.

  • Captive Castle (Development)

    A point-and-click game made in JavaScript for both Android and iOS.

    The goal is to find the relic stolen from your village. It takes place in a castle. You start at the front door and go through the different rooms picking up items to add to your inventory to be used later.

  • Pay in, Pay out: How to Create a Marketplace (Publication)
    Shopping online is more convenient than ever, so how do you create an online marketplace tailored to cater to your specific needs? In this article, Toptal JavaScript Developer Konrad Gadzinowski explores marketplace business models and payment methods for both regional and global services.
  • Trunk-based Development vs. Git Flow (Publication)
    In this article, Toptal Freelance Software Engineer Konrad Gadzinowski dissects trunk-based development and Git flow, listing the pros and cons for various use cases.
  • Creating Truly Modular Code with No Dependencies (Publication)
    Complex, tightly-coupled, and fragile interdependent code. We’ve all written it. The kind of code where fixing one bug creates seven more. Have you ever wondered how to create independent modular code? In this article, Toptal Freelance Software Engineer Konrad Gadzinowski walks us through the different types of architectural paradigms you can adhere to and how to write modular and decoupled code where changes to one module have minimal impact on the overall application.


  • Languages

    HTML/CSS, Bash, CSS, SCSS, TypeScript, Java, HTML5, JavaScript, Objective-C, SQL, C#, Swift
  • Frameworks

    Express.js, JUnit, Swagger, Bootstrap, Angular, Play Framework, YARN, ASP.NET
  • Libraries/APIs

    Socket.IO, jQuery, React, Node.js, Google Calendar API, Google Maps, Google Maps API, Backbone.js, Underscore.js, Stripe, Braintree API, Stripe API, Google AdWords, Vue.js
  • Tools

    Gulp.js, Git, Grunt, Packer, InVision, Adobe Flash, NPM, Flash, Illustrator CC, Photoshop CC
  • Paradigms

    REST, Responsive Web Design (RWD), Responsive, Design Patterns, Agile, MEAN Stack, UI Design, Concurrent Programming
  • Platforms

    Web, MacOS, Windows, Android, iOS, Amazon Web Services (AWS), Docker, Ubuntu, Meteor, MapBox, Azure, LAMP
  • Other

    Front-end, Back-end, APIs, Full-stack, Web Components, Analytics, Server Management, Neural Networks, BrainTree, Genetic Algorithms
  • Storage

    NoSQL, MongoDB, SQLite, MySQL, Elasticsearch


  • Master’s degree in Automatic Control and Robotics
    2011 - 2013
    Lodz University of Technology - Lodz
  • Bachelor's degree in Automatic Control and Robotics
    2007 - 2010
    Lodz University of Technology - Lodz

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