Robert Tessler - Full Stack & Mobile Developer

Full Stack Developer

Robert Tessler

******.*******@*******.***

+31-616-***-*** / Delft, NL

https://linkedin.com/in/roberttessler

https://github.com/rtessler

PROFESSIONAL SUMMARY

Senior Full Stack Developer with over 20 years experience developing enterprise systems. Specialising in Python, Javascript, Typescript, Node.js, React.js, SQL / NoSQL databases, AWS and AI/ML integration. Mobile development in Swift, SwiftUI, Kotlin, React Native and Flutter.

Able to architect event driven systems, work autonomously, communicate with clients, manage projects, mentor juniors and deploy quality applications across web and mobile platforms

KEY ACHIEVEMENTS

• Enhanced a SaaS cryptocurrency trading platform, delivering secure order management, real-time asset visualisation, and signup workflows.

• Optimised network data synchronisation and rendering performance for the QC One inspection app serving 18,000 active users, reducing load times and improving reliability across iOS and Android

• Engineered a cross-platform music streaming app featuring an intelligent cosine similarity song-matching algorithm to bridge Apple Music and Spotify playlists

• Designed and deployed a derivatives auto-trading desktop application in C++ used by traders globally at Deutsche Bank for automated opportunity spotting. SKILLS

Core Languages Python, Javascript, Typescript, Kotlin, C++, Java Frontend React.js, Next.js, Vue.js, Three.js, Unity Backend FastAPI, Node.js, Spring Boot, GraphQL, Kafka Mobile Swift / SwiftUI, Jetpack Compose, React Native, Flutter Database Postgres, MongoDB, Redis, SQLAlchemy

Cloud AWS (Lambda, S3, ECS), Firebase / GCP, Supabase Dev Ops & CI/CD Github Actions, GitLab pipelines, Docker, Kubernetes, Fastlane AI RAG pipelines, Langchain, MCP, Agent development Other System Architecture, Technical Lead, Agile Methodologies WORK EXPERIENCE

SixOfNine Engineering Delft, Netherlands

Founder, Project Manager, Developer Jul 2025 - present Permanent

• Digital consultancy providing software services and development of original products

• Engineered a Python/FastAPI/Django AI image processing service built on google gemini for advanced retail and commercial image applications

• Deployment of containerized services. Tech: AWS Lambda, S3, IAM, ECS, Docker and Kubernetes

• Development of mobile apps for image processing and offline music playback. Tech: Swift / SwiftUI, Android Kotlin, Jetpack Compose, bluetooth, MVVM

• Text to 3D model generation for architectural applications. Tech: RAG pipelines, Langchain, vector databases, MCP and agent development, Claude, Gemini, ChatGPT

• Frontend development in React.js, Vue.js, Typescript, OpenGL, QGIS, Three.js and Unity for interactive data visualisation

Poolder Rijswijk, Netherlands

Full Stack Developer Jan 2025 - Jul 2025

Contract

• Architected a SaaS crypto currency trading platform for managing client trades and assets. Tech: React.js, Next.js, TypeScript, Supabase backend API development, Postgres, Tailwind and ApexCharts.

• Streamlined the client signup workflow, reducing friction and improving conversion into active traders.

• Built secure admin tooling that gave operations staff real-time visibility and control over order monitoring and processing, reducing manual oversight effort.

• Designed intuitive data visualizations giving clients clear, real-time insight into their asset values and portfolio performance.

• Increased platform engagement and trust by introducing real-time buy/sell notifications and in-app messaging, keeping users informed and connected.

• Established a reliable, automated deployment pipeline, enabling faster and safer releases to production. Tech: GitLab pipelines, docker and Vercel. Sping Delft, Netherlands

Mobile Developer Sep 2023 - Sep 2024

Permanent

• Improved reliability and performance of the QC One inspection app, used daily by 18,000 active users, by optimising network data synchronization. Tech: React Native, Typescript, MobX, Realm DB, Sentry logging, Jest unit / integration testing

• Strengthened app stability and performance through improved state management, offline data storage, and proactive error monitoring.

• Boosted rendering performance to deliver a smoother, more responsive experience for users, and improved release confidence through comprehensive automated testing.

• Cut download and sync times for the Tessa Android app, improving user experience. Tech: Kotlin, Java, GraphQL, Coroutines, Flow, Room DB, Retrofit, Hilt, MVVM, Jetpack Compose and Clean Architecture

• Streamlined app store release management by automating build, testing, and deployment pipelines. Tech: GitHub actions CI/CD and Fastlane

• Led a research initiative into selective noise cancelling technology, exploring its feasibility and application for future product features. Tech: Python, FastAPI

• Built an energy usage calculator for the energy sector, translating complex consumption algorithms into an accessible, user-facing tool. Tech: Kotlin Sway Music London, Remote

Mobile Developer / Tech Lead Nov 2021 – May 2023

Contract

• Led development of a cross-platform music streaming app sharing playlists between Apple Music and Spotify — bridging two previously incompatible ecosystems. Tech: Swift, SwiftUI, Kotlin, Flutter, Firebase / GCP.

• Designed an intelligent song-matching algorithm using cosine similarity to accurately map tracks between platforms enabling cross-service playlist sharing.

• Delivered a polished, native-quality experience across iOS and Android, ensuring smooth audio playback regardless of platform.

• Enhanced user engagement by building real-time notifications, in-app chat, and live updates, turning a utility app into a social experience.

• Owned the product experience end-to-end — from Figma UI/UX design through to app store deployment and secure OAuth2-based account linking.

• Built and scaled the backend infrastructure supporting user data, image uploads, and cron scheduled background jobs, Tech Firebase / GCP, NoSQL database, Node / Express, Javascript, Python, OAuth, Google Vision API for image classification.

• Created an internal admin portal giving the team visibility into user activity and playlist generation, supporting data-driven product decisions. Tech: React.js KNAB Amsterdam

IOS Developer Apr 2021 - Aug 2021

Contract

Improved the KNAB banking app signup flow to increase client registrations. Use of IOS Swift, UIKit, Core Data, Reactive Programming, MVVM, OOP. Sublime X Sydney, Remote

Mobile Developer, Technical Lead May 2019 - Apr 2021 Permanent

• Developed a mobile Flutter app and admin web site in React.js / Redux for Marine Rescue NSW for reporting life threatening marine hazards in coastal waters. MRNSW Risk App.

• Created an IOS Swift app and React.js web app for Pepsi Cola Taste Challenge.

• Deployed to IOS and Android app stores

• API development in Firebase / GCP utilising Node.js, Express.js, Typescript and Python. Image upload, OAuth2 authentication, PDF generation.

• Did maintenance of the APTC Fiji technical college website. Tech: NET Core, C#, ASP.NET, .NET MVC, HTML, CSS, SASS and Sitefinity CMS.

• Implemented automated data processing and data upload into a Hubspot CMS for Crescent Wealth. Tech: Python, Pandas, shell scripts, Java, Spring Boot, Maven, Redis, Kafka messaging and AWS.

Saatchi & Saatchi Sydney, Australia

Full Stack Developer Mar 2018 - Apr 2019

Contract

• Built a React.js hearing test web app for Cochlear with Marketo and Salesforce REST API integrations; unit and integration tested with Jest.

• Developed a Node.js/Express.js API on AWS (S3, Lambda, API Gateway) for Toyota kiosk JSON data uploads.

Deloitte Sydney, Australia

Front End Developer Jan 2017 - Jan 2018

Contract

Delivered the Australian Tax Office Relationship Access Manager in Angular, TypeScript, RxJS and Bootstrap with Jasmine.js testing in an Agile team. Nielsen Sydney, Australia

Full Stack Developer Aug 2013 - Sep 2016

Permanent

• Built ad campaign analytics and an interactive page builder frontend in JavaScript, Angular, jQuery

• Handled deployment and scaling of the enterprise Java / Spring Boot / MySQL on AWS EC2.

Publicis Groupe Sydney, Australia

Full Stack Developer May 2011 - Jun 2013

Permanent

Built and enhanced client-facing .NET/ASP sites. Tech: C#, ASP.NET MVC, SQL Server, JavaScript, Backbone.js, jQuery.

Devotion Digital Sydney, Australia

Full Stack Developer Sep 2009 - Mar 2011

Permanent

Development and maintenance of multiple ASP.NET sites. Coding in Kentico CMS and .NET C#. Updated the wool.au website. Tech: Java, J2EE, Spring and WebSphere. Deutsche Bank Sydney, Australia

Desktop App Developer 2000-2005

Permanent

Created a derivatives auto-trading desktop app in C++ used by traders globally for automated opportunity detection.

EDUCATION

Graduate Certificate Applied Science, Bioinformatics, Sydney University Computer Science Honours, BSc, Sydney University

Bachelor of Science, BSc, Sydney University

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