Felix Hessenberger, Developer in Linz, Austria
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Felix Hessenberger

Verified Expert  in Engineering

Software Developer

Linz, Austria
Toptal Member Since
July 30, 2018

Inspired by the versat­ility and access­ibility of the web, Felix is always on the lookout for new challenges. His specialties are web, hybrid, and mobile apps as well as business software. Having worked at several startups, Felix is not afraid to take on projects by himself and also has valuable experience in areas like UX design and DevOps.


TimeSloth GmbH
TypeScript, React, Node.js, React Native
iOS, React, Android, Angular
Node.js, Java, MongoDB, Play! Authenticate, Scala, AngularJS




Preferred Environment

Git, IntelliJ IDEA, MacOS

The most amazing...

...thing I've developed is a timezone-aware rule-based date generation interface for a visitor management solution.

Work Experience


2019 - PRESENT
TimeSloth GmbH
  • Implemented extensive UI management with Material-UI.
  • Created a tenant-based shop plugin for customer websites.
  • Constructed a cross-platform app for scanning tickets.
  • Used Expo to distribute React Native over-the-air.
  • Utilized Yarn workspaces to manage a monorepo architecture consisting of seven packages.
Technologies: TypeScript, React, Node.js, React Native


2016 - PRESENT
  • Collaborated directly with small and medium clients.
  • Gained insight in different project management strategies.
  • Experienced some substantial growth first-hand.
  • Worked independently as well as within large teams.
  • Learned various UX and UI patterns.
Technologies: iOS, React, Android, Angular


2014 - 2015
  • Created a social network for photography.
  • Worked with a high volume of media content.
  • Designed a scalable architecture to handle load spikes.
  • Managed all technical communication and decision-making.
  • Integrated a web shop and payment system with the platform.
Technologies: Node.js, Java, MongoDB, Play! Authenticate, Scala, AngularJS

Graduate Research Assistent

2014 - 2014
University of Applied Sciences Upper Austria
  • Developed a matching algorithm to connect agencies and photographers.
  • Used semantic analysis to create a taxonomy of the agencies' requirements.
  • Used personalized metrics to learn photographers' specialities and preferences.
  • Designed a system to notify photographers about new briefings.
Technologies: AlchemyAPI, Scala

Full-stack Developer

2013 - 2014
Evntogram Labs GmbH
  • Created data-driven front-end views.
  • Applied usability and UX principles independently.
  • Collaborated closely with mobile developers.
  • Worked with scalable back-end environments.
  • Gained knowledge with database sharding and maintenance.
Technologies: Scala, MongoDB, Play! Authenticate, AngularJS

Web Developer

2012 - 2012
LimeSoda Interactive Marketing GmbH
  • Worked in a high-velocity agency environment.
  • Reworked the company website using a best practice approach.
  • Wrote custom CMS plugins in PHP.
  • Maintained extensive enterprise websites.
  • Serviced running systems remotely using SSH.
Technologies: jQuery, TYPO3, WordPress, PHP


Starting as a pet project, Felix developed a complementary suite of applications for end-to-end visitor management and ticketing.
The biggest product is a calendar-based manager UI where template-based events can be created and bookings can be managed. The second application is a shop plugin that customers can integrate into any website. Lastly, a React Native-based scanner app is made available to customers on iOS and Android.
Felix wrote the project exclusively in TypeScript, it runs on the Google Firebase platform and has a server back-end with Node.js. The code is shared between projects via the monorepo pattern.

Swilox iOS App

A native iOS app written in Swift that serves as a factor for the Swilox identity service.
Due to the nature of the app, there is a big focus on security. The server-client communication is done via a custom reactive protocol. Other interesting aspects of the app include hardware security via Secure Enclave as well as biometric authentication via LocalAuthentication.


A React Native app uses a single codebase to build clients for three platforms—iOS, Android, and Web. The product is backed by Firebase Cloud Firestore and Cloud Functions. The app was planned with a strong focus on economic operation and maximum scalability. Features include signed PDF generation and cryptographic handshaking.

Bee Meaningful

Bee is a social network written in React and backed by Firebase.
The web app and design system were refactored to satisfy modern standards. Also, real-time interactivity was added to improve user satisfaction. The project was realized with a growing number of users in mind, so scalability and accessibility were a top priority.

Imofix Cockpit

A white-labeled React app that enables renters to report various issues to their service provider.
The app is interesting in the way that it combines server- and client-side rendering approaches. A back-end cockpit enables facility managers to search for issues via Algolia.

Heat Pump Configurator

An Angular app to automate offer generation using the client's complex business logic. The step-based configuration interface is driven by data uploaded in the back-end application via Excel files. The offers can be saved and exported as PDFs, which are generated via a Firebase cloud function using Puppeteer.

Presono Platform

Presono is a platform for managing presentations in enterprise environments.
Supporting their agile team, I developed a template-based WYSIWYG editor for presentation slides as well as many other parts of the React-based web platform. Additionally, I developed an offline-capable iOS wrapper for the core platform.

Presono Contacts

Part of the Presono platform, Presono Contacts is a flexible CRM front-end for fairs and other events.
I developed this native iOS app using the Eureka Forms library. With a data-driven UI and complex nested navigation patterns, the app grew into a complex project.

Lime Inventory

An iOS and Android app for managing bar inventory written in React Native.
The app features many CRUD operations and a multi-tenant user model. At the core, a visual fill level input module enables the user to efficiently input data.


A platform that connects photographers and agencies based on their interests and location.
I developed the web-based platform by myself using AngularJS in the front end and the Play framework in the back end.

ADC Fuel

iOS and Android apps to inform truck drivers of nearby fuel-related deals and promotions.
The user-facing views are web-based and written in React and the core functionality and wrapper are written in native code.

Small Batch Learning App

A simple React Native app that enables users to consume educational content.
2012 - 2014

Master's Degree in Interactive Media

University of Applied Sciences Upper Austria - Hagenberg, Austria

2009 - 2012

Bachelor's Degree in Media Technology and Design

University of Applied Sciences Upper Austria - Hagenberg, Austria


React, Node.js, REST APIs, jQuery, Play! Authenticate, Vue


Expo.io, Git, IntelliJ IDEA, RabbitMQ


React Native, Redux, Angular, AngularJS, Play Framework, Express.js, Next.js, Flutter, TYPO3, Play, Cypress


CSS, HTML, Java, JavaScript, TypeScript, Scala, Kotlin, Swift, SQL, Sass, PHP


RESTful Development, Cross-platform, Object-oriented Programming (OOP), UI Design, Agile Software Development, Functional Programming, Object-relational Mapping (ORM), Concurrent Programming


Firebase, iOS, Amazon Web Services (AWS), Android, Heroku, MacOS, WordPress, AlchemyAPI


MongoDB, Redis, Google Cloud, NoSQL, MySQL, Redis Cache


Hybrid Apps, User Experience (UX), User Interface (UI), Mobile First, Cryptography, Front-end Development, Customer Relationship Management (CRM), Material Design

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