Bartosz Wesołowski, Developer in Poznań, Poland
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Bartosz Wesołowski

Verified Expert  in Engineering

Software Developer

Poznań, Poland
Toptal Member Since
September 29, 2014

Bartosz is an Android developer with 9+ years of experience in product companies and software houses. He has worked as a web developer (Java, PHP, JavaScript, CSS) and desktop app developer (C++). Bartosz knows the basics of iOS development, has a couple of his apps on Google Play, and has created some Unity games as a hobby.


Android, Kotlin, Android Studio, Git, GitHub, Cloud Firestore, SQL, JSON...
Android, Android Studio, Kotlin, Git, GitHub, Buildkite...
Android, Java, Kotlin, Android Studio, Firebase, Git, GitHub, Bitbucket...




Preferred Environment

Git, Android Studio, Kotlin, MacOS, Gradle

The most amazing...

...thing I've coded was an AI bot for the Dyna Blaster game that beat its competitors to win an AI contest.

Work Experience

Senior Android Developer

2022 - PRESENT
  • Worked as a solo developer on an event ticketing app.
  • Handled the whole development process and published the app to Google Play.
  • Introduced Cloud Firestore, which greatly improved the app's performance.
Technologies: Android, Kotlin, Android Studio, Git, GitHub, Cloud Firestore, SQL, JSON, Firebase Analytics, Gradle, RxJava, MacOS, Android Jetpack, Google Play Console, Google Play Store, Crashlytics

Staff Software Engineer

2022 - PRESENT
  • Added new features to the app via A/B tests to determine their viability.
  • Developed multiple technical improvements in the app.
  • Led some of the projects in a cross-functional team of developers.
Technologies: Android, Android Studio, Kotlin, Git, GitHub, Buildkite, Agile Software Development, SQL, Java, JSON, Gradle, RxJava, Coroutines, MacOS, Android Jetpack, Google Play Console, Google Play Store, Swift, Crashlytics, Jetpack Compose

Senior Android Developer

2017 - 2022
  • Developed the largest eCommerce app in Poland with around 8 million monthly active users.
  • Took charge of the app's architecture and developer tools.
  • Worked as a part of the original core/platform team created to fight tech debt.
  • Acted as a presenter at internal conferences and talked about internal tools and best practices.
Technologies: Android, Java, Kotlin, Android Studio, Firebase, Git, GitHub, Bitbucket, Agile Software Development, Python, SQL, JSON, Firebase Analytics, Gradle, RxJava, Coroutines, MacOS, Android Jetpack, Google Play Console, Google Play Store, Crashlytics

Senior Android Developer

2020 - 2021
  • Developed new features in a cryptocurrency app.
  • Learned basic information about blockchain and cryptocurrencies.
  • Collaborated with a completely remote team.
Technologies: Android, Kotlin, Coroutines, Android Studio, Gradle, Git, Agile Software Development, SQL, JSON, Firebase Analytics, RxJava, MacOS, Android Jetpack, Google Play Console, Google Play Store, GitHub, Crashlytics

Android Developer

2015 - 2017
  • Worked on around 200 Wikia community apps released from a common codebase.
  • Developed a new UI test system to reduce bugs.
  • Worked in an international environment using English as the primary language.
Technologies: Android, Gradle, Java, Android Studio, Agile Software Development, Python, JSON, RxJava, MacOS, Google Play Console, Google Play Store, GitHub, Crashlytics

Android Developer

2015 - 2015
STX Next
  • Developed a banking app for one of Poland's largest banks.
  • Collaborated with a team of developers, designers, and testers.
  • Used Scrum to manage the product's development.
Technologies: Java, Android, Eclipse, Gradle, Agile Software Development, JSON

Associate Consultant

2014 - 2015
  • Developed an internal app for room booking using Xamarin.
  • Trained other developers in Android app development.
  • Learned Xamarin and C# development.
Technologies: Android, Java, Xamarin, C#, Visual Studio, Eclipse, JSON

Android Developer

2013 - 2013
  • Created the whole app by myself (I was the only developer).
  • Collaborated with a graphic designer on the app's UI and UX.
  • Worked remotely, collaborating with colleagues from a variety of countries through Skype communication.
  • Approved the app's final look and functionality.
  • Implemented Gmail authentication using built-in Android mechanisms so users would not need to input a username or password.
  • Implemented the email synchronization using SMTP and IMAP on Android.
Technologies: Git, Eclipse, Java, Android, JSON

Web Developer

2012 - 2013
  • Created a real estate selling/renting portal.
  • Collaborated with a graphic designer, implementing his ideas and suggesting changes.
  • Used Basecamp to coordinate work, schedule work and discuss problems/ideas.
  • Designed and implemented the database.
  • Collaborated with mobile developers to create web services that they could use in the apps.
Technologies: Git, SQL, REST, JavaScript, CSS, HTML, PHP, JSON

Web Developer

2012 - 2012
Kraupe Studio
  • Created a website for an architecture firm.
  • Collaborated with a designer on the site's UI.
  • Worked from home, but engaged in occasional face-to-face meetings with the client.
  • Created the site in a way that can be maintained by non-technical people.
  • Used basic SEO techniques to boost the site in search engines.
Technologies: JavaScript, CSS, HTML, JSON

PHP Developer

2012 - 2012
  • Worked on a portal for school children allowing them to learn mathematics in a fun way.
  • Collaborated with graphic designers to cut and implement their designs on the portal.
  • Worked mostly from home with weekly organizational meetings.
  • Used Scrum to plan and evaluate the work.
  • Took part in the planning process of designing the missing functionality and deciding on different approaches.
Technologies: JavaScript, CSS, HTML, PHP, JSON

Software Developer

2011 - 2012
Poznan Supercomputing and Networking Center
  • Worked on a digital library portal.
  • Designed and created the UI for the portal.
  • Worked on the Single Sign On mechanism.
  • Created some of the knowledge base acquisition algorithms.
  • Represented the company during a large local event, explaining the details of the project on an early prototype.
Technologies: SQL, REST, JavaScript, CSS, HTML, JSON

C++ Developer

2009 - 2010
  • Developed software for large retail stores.
  • Detected and fixed bugs reported by users.
  • Prototyped an online store.
  • Used Python scripts to automate boilerplate code creation.
  • Refactored a large portion of outdated and messy code.
Technologies: C#, Python, C++

Junior Software Developer

2007 - 2007
  • Worked on a mobile car navigation app.
  • Created an internal tool for visualizing car speed on the map.
  • Worked with multiple phone brands and operating systems.
  • Learned about GIS and digital maps.
  • Improved the navigation algorithm by taking traffic information into account.
Technologies: C++, Java

Blobby Volley
A beach volleyball Unity game—a remake of a cult video game—that lets players compete against AI or human opponents. It has two unique visual themes and five difficulty levels. It has 500,000+ downloads.

Milan Metro
A metro map of the Milan urban network. It lets you search for stops, uses vector graphics for high-quality zooming, and integrates AdMob banner ads. It utilizes benchmark profiles for faster app launches. It has around 20,000 active users on Google Play.

Blog Stats
An Android utility app that lets you see your blog's daily, weekly, and all-time visits. It uses Google APIs to let you log in without typing your username and password. It was my playground for Jetpack Compose and Kotlin coroutines.

A cryptocurrency wallet app that lets you send and receive crypto transfers. It helps you stay up to date with recent crypto news. It can be used for staking too. It has very low fees, and you can import your existing wallets.

The biggest eCommerce app in Poland (bigger than Amazon and eBay combined). I was part of the core team handling the app's architecture, removing legacy code, developer tools, automated tests, CI/CD, etc.


Java, Kotlin, SQL, Python, C#, Swift, C++, JavaScript, HTML, CSS, PHP


RxJava, Google API, OpenGL


Android Studio, Git, Crashlytics, Gradle, Firebase Analytics, Android Jetpack, Visual Studio, GitHub, Bitbucket


Android, Firebase, MacOS, Xamarin, Eclipse, Buildkite


REST, Agile Software Development


JSON, Cloud Firestore


Coroutines, Jetpack Compose, SVG, Google Play Console, Google Play Store, Programming, Games, 2D Games


Unity, JUnit, Espresso

2004 - 2009

Master's Degree in Computer Science

Poznan University of Technology - Poznań, Poland

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