Jan-Hendrik is currently unavailable
Jan-Hendrik de Vaal
Verified Expert in Engineering
Android Developer
Cape Town, Western Cape, South Africa
Toptal member since February 9, 2021
Bio
Jan-Hendrik is a senior Android and Kotlin multiplatform engineer with 19 years of experience building high-performance consumer apps — from Bluetooth LE and IoT devices to media-rich streaming, edutainment, and eCommerce platforms. His work has won at the Kidscreen Awards and the SA eCommerce Awards. He takes projects from rough idea to app store, and specializes in shared Kotlin codebases that scale cleanly across platforms.
Portfolio
Combustion LLC
Kotlin, Android, Jetpack Compose, Android App Development, Mobile, Android API...
Paramount
Android, Kotlin, RxJava 2, RxKotlin, Retrofit 2, Room, Coroutines, Dagger 2...
Learning Tapestry
Android, Kotlin, Mobile
Experience
- Android - 14 years
- Java - 14 years
- OkHttp - 9 years
- Retrofit - 9 years
- RxJava - 9 years
- Kotlin - 8 years
- Dagger - 4 years
- Coroutines - 3 years
Work Experience
Android Developer
2024 - PRESENT
Combustion LLC
- Added support for new smart devices to the app. This includes UI, direct BLE communication with devices, and cloud sync of device state.
- Enhanced device graphs with scrubbing, zoom, and per-sensor visibility, significantly improving data exploration and user insight.
- Migrated device data point logs from in-memory storage to a database-backed model, improving performance, memory efficiency, and scalability.
Technologies: Kotlin, Android, Jetpack Compose, Android App Development, Mobile, Android API, Bluetooth, Firebase, Amazon Web Services (AWS), GraphQL
Senior Android Engineer
2021 - PRESENT
Paramount
- Implemented new features like APIs to track children's learning progression in Paramount's Noggin app, a subscription service for preschool videos, e-books, learning games, and interactive episodes.
- Was chosen from Noggin's original development team to contribute to the development of a new, more immersive version of the app, recognizing my technical proficiency and past contributions.
- Served as the primary developer who implemented the new app's video player and casting functionality.
- Won Best Branded Learning App at the 2024 Kidscreen Awards for the new Noggin app.
- Worked as the primary developer who maintained and optimized the TV apps, ensuring seamless user experiences.
- Established coding standards and architectural patterns that increased the crash-free rate from 95% to over 99%.
Technologies: Android, Kotlin, RxJava 2, RxKotlin, Retrofit 2, Room, Coroutines, Dagger 2, Model View ViewModel (MVVM), Hilt, Jetpack Room, Jetpack Compose, Dependency Injection, Model View Intent (MVI), Android SDK, Android Studio, Android TV, Mobile Development, Mobile App Development, Mobile APIs, Mobile, Mobile UX, Mobile UI, REST, Android App Development
Android Developer
2021 - PRESENT
Learning Tapestry
- Consulted on implementing Learning Tapestry's content in Paramount's Noggin app.
- Collaborated on implementing Learning Tapestry's APIs and learning analytics in the Noggin app.
- Worked on the architecture of the new, more immersive version of the Noggin app.
Technologies: Android, Kotlin, Mobile
Senior Android Developer
2020 - 2021
Teamwork.com
- Developed Teamwork's native Android rewrite of their legacy cross-platform mobile app for their task management and team collaboration software product.
- Fixed bugs in the chat app that allows teams to communicate and collaborate.
- Managed a team of developers to achieve the sprint goal.
Technologies: Android, Kotlin, Dagger, OkHttp, Retrofit, Hilt, Jetpack Room, Room, RxJava, RxJava 2, RxKotlin, Dependency Injection, Dagger 2, Mobile Development, Mobile App Development, Mobile APIs, Android SDK, Android Studio, Android App Development, Mobile, Mobile UX, Mobile UI, REST
Lead Android Developer
2016 - 2020
Flat Circle
- Developed and architected Android apps for multiple clients across various fields, including smart devices, eCommerce, finance, project management, logistics, delivery, and news media.
- Consulted on the development of the Android launcher and media player software used on the Marshall London Android phone, which, according to The Verge, is "one of the best low-end phones we've seen."
- Mentored junior Android staff on the best architecture and design principles.
Technologies: Android, Kotlin, Java, RxJava, Retrofit, OkHttp, Coroutines, Internet of Things (IoT), Model View ViewModel (MVVM), RxJava 2, RxKotlin, GraphQL, Dependency Injection, Mobile App Development, Mobile Development, Mobile APIs, Android SDK, Android Studio, Android App Design, Android App Development, Android TV, Mobile, Bluetooth, GPS, Firebase, Mobile UX, Mobile UI
Senior Android Developer
2015 - 2016
Spree
- Developed and architected Spree's fashion eCommerce Android app with a magazine-styled shopping experience as the sole developer.
- Released the app ahead of schedule and on time for Black Friday to get considerable conversion rates.
- Contributed to the design and UX planning of the app.
Technologies: Android, Groovy, Java, RxJava, Retrofit, RxJava 2, OkHttp, Mobile APIs, Android SDK, Android Studio, Android App Design, Android App Development, Mobile, REST, Mobile UX, Mobile UI
Senior Mobile Developer
2013 - 2015
Takealot
- Remastered Takealot's outdated, outsourced Android app, which became South Africa's number one eCommerce app.
- Developed all non-UI aspects of the new mobile site in 2015.
- Won the Best eCommerce Mobile Site Award at South Africa's eCommerce Awards 2015 for the new mobile site I developed.
Technologies: Android, Java, JavaScript, Android SDK, Android Studio, Mobile APIs, Android App Design, Android App Development, Mobile, REST, Mobile UX, Mobile UI
Senior Software Developer
2010 - 2013
Virtual Mobile Technologies
- Developed VMT's product RAMP, a secure mobile enterprise application platform aimed at managing the complete enterprise environment required to create, deploy, and manage secure native cross-platform mobile applications.
- Created and maintained RAMP virtual machines across various platforms, including Android, iOS, HTML5, Windows Phone, BlackBerry, and Java ME.
- Assisted the clients in developing apps that use the RAMP platform.
Technologies: Java, Java ME, Android, C#, JavaScript
Software Developer
2007 - 2010
Perceive
- Created monitoring software for Perceive's intelligent surveillance product.
- Developed various surveillance algorithms for the system, such as human detection and fall detection.
- Implemented the communication between the server and monitoring software.
Technologies: Python, OpenCV, NumPy
Project History
Noggin Preschool Learning Games and Videos for Kids
Noggin is an Android app from ViacomCBS that provides preschoolers with an entertainment and education subscription service led by Nick Jr. characters. The service gives access to a library of videos, games, and e-books.
My main responsibility was implementing learning analytics and content in the app.
My main responsibility was implementing learning analytics and content in the app.
Takealot Mobile Shopping App
https://play.google.com/store/apps/details?id=fi.android.takealotAndroid app for Takealot.com, South Africa's number one shopping site. I was the company's first in-house Android developer, and I liaised with designers to remaster the outdated, outsourced app with a modern UI and improved user experience.
Good Old GOG App
An Android app that is a faster and more user-friendly alternative to GOG's mobile website, www.gog.com. GOG is a digital distribution platform with a curated selection of video games. I casually developed the app in my free time, and it has grown to over 50,000 installs.
Teamwork App
https://play.google.com/store/apps/details?id=com.teamwork.mobile.projectsThe new native Android app for Teamwork's project management product helps managers, staff, and clients work together more productively and efficiently. I was one of the Android developers on the new app.
Sunday Times Daily App
Android news app that provides subscribers with daily curated editions of opinion pieces, local news, and world news. I was part of the team that developed the news app SDK used by the app owner to build app versions of its news publications and develop this implementation of the SDK.
Ask Mechanicus Lovecraft
https://github.com/jhavatar/AskMechanicusLovecraftWhat if Lovecraft was a member of the Adeptus Mechanicus and an AI chatbot you could use to ask questions?
This messaging app, backed by the OpenAI API, allows you to ask Mechanicus Lovecraft, the AI assistant, questions.
This messaging app, backed by the OpenAI API, allows you to ask Mechanicus Lovecraft, the AI assistant, questions.
Marshall London Android Phone's Launcher and Media Player
The Marshall London phone was a unique Android handset aimed at audiophiles. It was developed by the Marshall company, known for their amplifiers, and released in 2015. The London phone is "one of the best low-end phones we've seen," according to The Verge.
The device's launcher and media player were outsourced to the agency Flat Circle, where I consulted on and initialized the development.
The device's launcher and media player were outsourced to the agency Flat Circle, where I consulted on and initialized the development.
Combustion Inc. Android App
https://play.google.com/store/apps/details?id=inc.combustion.appThe Combustion App is the official Android companion app for Combustion's smart devices, letting you monitor real-time cooking temperatures, view live graphs, see doneness predictions, and control thermometer settings directly from your phone throughout the entire cook.
Big Box Chaser
https://bigboxchaser.com/A personal catalog for your PC big box game collection. Search a comprehensive game database, add titles to your shelf, and browse your collection with rich cover art — including an interactive 3D box viewer.
Education
2005 - 2008
Master of Science in Engineering Degree (MScEng) in Applied Mathematics
Stellenbosch University - Stellenbosch, South Africa
2004 - 2004
Bachelor of Science with Honours Degree (BScHons) in Computer Science
Stellenbosch University - Stellenbosch, South Africa
2001 - 2003
Bachelor of Science Degree (BSc) in Mathematical Sciences
Stellenbosch University - Stellenbosch, South Africa
Skills
Libraries/APIs
RxJava, Retrofit, Retrofit 2, RxJava 2, RxKotlin, Jetpack Room, Android API
Tools
Android Studio, Android Jetpack
Languages
Kotlin, Java, JavaScript, Groovy, GraphQL, C#
Frameworks
Android SDK, Dagger, Dagger 2
Platforms
Android, Java ME, Android TV, Mobile, Firebase, Amazon Web Services (AWS)
Paradigms
Dependency Injection, Model View ViewModel (MVVM), Model View Intent (MVI), Mobile Development, REST
Storage
Realm
Other
Mobile Applications, OkHttp, Coroutines, Room, Internet of Things (IoT), Hilt, Jetpack Compose, Mobile App Development, OpenAI, Live Chat, Messaging, Mobile APIs, Android App Design, Android App Development, Bluetooth, GPS, Mobile UX, Mobile UI, Kotlin Multiplatform
Collaboration That Works
How to Work with Toptal
Toptal matches you directly with global industry experts from our network in hours—not weeks or months.
1
Share your needs
Discuss your requirements and refine your scope in a call with a Toptal domain expert.
2
Choose your talent
Get a short list of expertly matched talent within 24 hours to review, interview, and choose from.
3
Start your risk-free talent trial
Work with your chosen talent on a trial basis for up to two weeks. Pay only if you decide to hire them.
Top talent is in high demand.
Start hiring