Maciej Korzeniewski, Developer in Pyla, Larnaca, Cyprus
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Maciej Korzeniewski

Verified Expert  in Engineering

Mobile Developer

Pyla, Larnaca, Cyprus
Toptal Member Since
July 5, 2022

Maciej is an experienced mobile developer skilled in Flutter, iOS (Objective-C/Swift), and Android (Java/Kotlin) app development. He excels in setting up CI/CD pipelines with Bitrise/Codemagic for automated building, testing, and deploying to app stores. Maciej is well-versed in Firebase products like Firestore, Crashlytics, and Authentication. He also has experience in Node.js and TypeScript for server-side applications and uses React for web development.



Preferred Environment

MacOS, Slack, Flutter, Firebase, TypeScript, Node.js

The most amazing...

...thing I've done was leading and developing Hamilton — The Official App, available for both Android and iOS.

Work Experience

Native Swift/Kotlin Developer

2023 - 2023
Visible - Activity tracking for Long Covid and ME/CFS
  • Built a premium feature that allows the Visible app users to gather health-related data from Polar devices using Polar SDK.
  • Implemented storing health-related data in an encrypted, on-device database.
  • Executed uploading health-related data to the back end.
  • Implemented the Python back end running on Google Cloud Run that processes uploaded health-related data and calculates metrics based on it.
Technologies: Swift, Kotlin, Flutter

Flutter/Swift/Kotlin SDK Developer

2022 - 2023
beaconsmind AG
  • Implemented binding for Flutter/React Native/Ionic in iOS/Swift and Android/Kotlin for the company's SDK.
  • Developed pipelines that automate deployments of multiple native iOS and Android apps, saving the company a lot of time and cumbersome work as it was done manually before.
  • Designed a user-friendly flow to request permissions required by the SDK (Bluetooth, location, and notifications).
Technologies: Flutter, Dart, iOS, Android, React Native, Ionic, Swift

Tech Lead

2021 - 2022
Very Good Ventures
  • Led the re-architecture of the Hamilton Musical app.
  • Co-developed an open-source web project called Photobooth for the Google I/O event. It allowed people to take a photo, add assets and share it with friends on social media.
  • Co-created apps for Homethrive Inc. with incorporated video streaming using Twilio SDK.
  • Improved testing skills by providing the apps with 100% test coverage.
  • Deployed apps to the App Store and Google Play Store using phased or incremental rollout.
Technologies: Flutter, Firebase, Mobile, Mobile Development, Figma, Minimum Viable Product (MVP), Dart, REST APIs

Mobile Developer

2020 - 2021
  • Contributed to the development of a home budget assistance app.
  • Developed the mobile app with fine-grained UI using Flutter.
  • Designed the offline-first architecture based on Firebase Firestore.
  • Added authentication with external providers (Google, Facebook, and Apple).
  • Implemented a recommendation system based on Firebase Dynamic Links.
  • Incorporated a premium subscription program using IAPs (Apple Pay and Google Pay).
Technologies: Flutter, Firebase, Mobile, Mobile Development, Minimum Viable Product (MVP), Dart, REST APIs

Mobile Developer

2016 - 2020
  • Implemented a GPS tracking module for Android in Kotlin.
  • Co-created Activity Challenges, an activity GPS tracker and game, with React Native and Redux.
  • Developed the Shell Fleet Assistant, a fleet management app in Xamarin and MvvmCross.
  • Added real-time chat functionality with React Native, Redux, and Firebase Firestore for BeautyClick, a finding beauty specialist app.
Technologies: Flutter, Firebase, React Native, Xamarin, .NET Core, React, Redux, Mobile, Mobile Development, Figma, Minimum Viable Product (MVP), Fitness, REST APIs

Hamilton Flutter Mobile App
As a tech lead, I led the comprehensive overhaul of the Hamilton app, completely revamping its architecture and user interface to enhance user experience and performance. This involved implementing a multi-layer reactive architecture that leverages caching mechanisms to minimize the app's reliance on Firestore reads. Leading a talented team of 3 to 6 mobile developers, I ensured seamless collaboration throughout the development process. Rigorous testing was a top priority, achieving a remarkable 100% test coverage to guarantee the app's reliability. To maintain code quality, I established GitHub pipelines that included static code analysis, formatting checks, and rigorous testing procedures before merging any code changes. I streamlined the deployment process by setting up automatic store deployment pipelines using Codemagic and employed a phased rollout strategy when launching updates. Post-release, I diligently maintained the app, addressing low-level native and memory-related issues to ensure a smooth and stable user experience.

You can find the app on Google Play here: and on the App Store here:

Flutter/Swift/Kotlin SDK Development

As a developer, I was in charge of implementing Flutter SDK in Dart, Swift, and Kotlin for the client's native SDK related to beacon scanning. I was also involved in fixing bugs in the native SDK itself. I created a demo application in Flutter that showcased the functionalities of the SDK.

I also developed pipelines to automate deployments of multiple apps that the company owns.

Home Budget Assistance App
As a mobile developer, I created a mobile app with a polished user interface using Flutter. I designed an offline-first architecture based on Firebase Firestore. I added authentication with external providers like Google, Facebook, and Apple. I implemented a recommendation system using Firebase Dynamic Links. I included a premium subscription program using IAPs (Apple Pay and Google Pay).

Native Swift/Kotlin developer integrating with health armband
I successfully implemented a premium feature within the Visible app, enabling users to seamlessly collect health-related data from Polar devices through the integration of the Polar SDK. Furthermore, I ensured the secure storage of this sensitive information within an encrypted on-device database, prioritizing user data privacy and security. To facilitate data analysis and insights, I also implemented a robust data pipeline, allowing the app to efficiently upload health-related data to our backend infrastructure. This backend, powered by a Python application running on Google Cloud Run, processes the incoming data, computes relevant health metrics, and provides users with valuable insights based on their personal health data.
2020 - 2020

Master's Degree in Computer Science

Technical University of Denmark - Denmark

2015 - 2019

Bachelor of Engineering Degree in Computer Science

Warsaw University of Technology - Warsaw, Poland


REST APIs, Node.js, React




Flutter, Redux, React Native, .NET Core, Ionic


Mobile Development, Testing


Dart, TypeScript, Swift, Kotlin, Python


Firebase, Mobile, Xamarin, iOS, Android


Cloud Firestore


Deployment, Crash Reporting, Crash Fixing, Minimum Viable Product (MVP), Automated UI Testing, Code Coverage, Fitness, Data Structures, Networking

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