Stefan is available for hire
Hire StefanStefan Trost
Verified Expert in Engineering
Front-end Developer
Stuttgart, Baden-Württemberg, Germany
Toptal member since February 16, 2022
Bio
Stefan is a developer with 5+ years of commercial experience specializing in front-end and mobile development, conceptual design, planning, and prototyping. His technical expertise includes React, JavaScript, TypeScript, and Node.js. Stefan's industry experience is backed by a bachelor's degree in business informatics. A Certified Scrum Master, he is fascinated by technology and its possibilities and is highly motivated to leverage it to deliver customer and business value.
Portfolio
LawGames GmbH
Google Cloud Platform (GCP), Google Cloud, CTO, Planning, IT Project Management...
Self-employed
React Native, React, TypeScript, Ionic, Angular, WordPress, Balsamiq...
LawGames GmbH
JavaScript, TypeScript, Python, Retrieval-augmented Generation (RAG)...
Experience
- React Native - 5 years
- Firebase - 5 years
- JavaScript - 5 years
- Git - 5 years
- Google Cloud - 4 years
- React - 3 years
- Redux - 3 years
- TypeScript - 2 years
Preferred Environment
MacOS, Visual Studio Code (VS Code), Git, Firebase, Google Cloud, JavaScript, TypeScript, React, React Native, Docker, Cursor AI, AI Tools, Claude
The most amazing...
...project I've been involved in is planning, designing, and implementing a web and mobile application from the ground up for a startup.
Work Experience
Interim CTO
2025 - PRESENT
LawGames GmbH
- Co-designed a new white-label learning platform from scratch in close collaboration with the Business Owner, translating business ideas into a scalable technical architecture.
- Led end-to-end architectural decisions, including multi-tenancy vs. single-tenancy models, CMS design, data separation, scalability, and deployment strategies.
- Acted as the primary technical advisor, evaluating feasibility, trade-offs, and long-term maintainability of platform decisions.
- Implemented the complete platform stack independently from the ground up, including CMS, back-end services, and client applications.
- Built a white-label CMS allowing each customer to manage their own content, distributed to branded client apps for end users.
- Developed and maintained the React Native application, contributing significantly to UI/UX design and overall user experience.
- Engineered an AI-powered tutor using RAG technology to query and reason over 22,000 legal documents.
- Designed and operated the full cloud infrastructure on Google Cloud Platform (Cloud Run, VMs, load balancing, backups).
- Architected and implemented a robust CI/CD pipeline with separated dev, staging, and production environments, reducing release cycles by over 65% and enabling automated app store deployments.
Technologies: Google Cloud Platform (GCP), Google Cloud, CTO, Planning, IT Project Management, Leadership, Multi-tenant SaaS, Multi-tenant Architecture, System Architecture, Software Architecture, React, Next.js, TypeScript, Tailwind CSS, GitHub, GitHub Actions, Docker, Cloud Run, Deployment, CI/CD Pipelines, Testing, Unit Testing, Jest, Storybook, Turborepo, Monorepos, Prisma, PostgreSQL, AI Tools, Claude, Model Context Protocol (MCP), App Store, Expo, Cross-platform App Development
Senior Full-stack Developer and IT Consultant
2012 - PRESENT
Self-employed
- Led multiple full-stack projects from concept to production.
- Transformed client business requirements into scalable technical solutions.
- Consulted clients on selecting the right technologies for their specific needs.
- Mentored junior developers, sharing knowledge and guiding their professional growth.
- Played a key role in the recruitment of developers, ensuring a skilled and cohesive team.
- Developed robust web applications, aligning with the client's business goals and user needs.
- Crafted high-quality mobile applications, focusing on performance and user experience.
- Designed and implemented cloud infrastructures, primarily using AWS and Google Cloud.
- Planned and built applications from scratch, focusing on scalable and maintainable code.
- Established deployment pipelines, streamlining the release process for applications.
Technologies: React Native, React, TypeScript, Ionic, Angular, WordPress, Balsamiq, Adobe Experience Design (XD), Prototyping, Front-end, Mobile App Development, Software Development, HTML, CSS, GitHub, Visual Studio Code (VS Code), Amazon Web Services (AWS), iOS, HubSpot CRM, Camera API, Google Cloud Functions, Back-end, Full-stack, HTML5, TypeScript 3, Python, Next.js, User Experience (UX), FastAPI, MongoDB, Zustand, RESTFul APIs, SaaS Design, System Architecture, Full-stack Development, HubSpot API, User Interface (UI), Automation, OpenAI API, ChatGPT, ChatGPT API, Chatbots, Artificial Intelligence (AI), Large Language Models (LLMs), Testing, Unit Testing, Cloud, Android, E2E Testing, Detox, CI/CD Pipelines, OpenAI GPT-3 API, OpenAI GPT-4 API, APIs, Mobile Development, Mobile, API Integration, MERN Stack, Shadcn, React Query, Cursor AI, AI Tools, Claude, Model Context Protocol (MCP), App Store, Expo, Application State Management, Cross-platform App Development, Google Play Store
Lead Architect & Mobile Developer
2024 - 2025
LawGames GmbH
- Enhanced internal app search functionality, boosting response times by 93% for end users.
- Developed an interactive AI bot enabling users to effectively learn legal definitions.
- Engineered an AI tutor leveraging innovative AI and RAG technology to query over 22,000 documents for qualified legal answers.
- Optimized overall application performance through targeted refactoring and improvements.
- Contributed significantly to the UI/UX design and development of the React Native application.
- Managed and maintained the Google Cloud Platform infrastructure, including setting up and deploying VMs, configuring and managing Cloud Run services, and implementing load balancing and backup strategies.
- Architected and implemented a comprehensive CI/CD pipeline, slashing release times by two-thirds by introducing distinct development, testing, and production environments and enabling automated app store deployments.
- Played a key role in the planning and architectural design for new application features.
Technologies: JavaScript, TypeScript, Python, Retrieval-augmented Generation (RAG), React Native, Artificial Intelligence (AI), Large Language Models (LLMs), Firebase, LangChain, Chatbots, Portkey.ai, ChatGPT, ChatGPT API, OpenAI API, Google Cloud Platform (GCP), CI/CD Pipelines, Deployment, Automation, Bitrise, App Store Deployment, Architectural Design, CTO, Fractional CTO, User Interface (UI), Code Review, Team Mentoring, Testing, Unit Testing, Cloud, Full-stack, Android, E2E Testing, Detox, OpenAI GPT-3 API, OpenAI GPT-4 API, APIs, Mobile Development, Mobile, UX Design, API Integration, Shadcn, AI Tools, AI Agents, Claude, App Store, Expo, Cross-platform App Development, Google Play Store
Senior Full-stack Developer
2024 - 2024
Plana Earth GmbH
- Developed a responsive micro-front end with a modern single-spa architecture.
- Implemented a comprehensive test suite using test-driven development.
- Refactored and optimized the front-end architecture to improve scalability and maintainability.
- Collaborated with cross-functional teams, including the front-end, back-end, data, design, and product teams, to make pragmatic decisions and contribute to technology and architecture decisions.
- Improved the release process by introducing multiple CI/CD pipelines to automate the deployment process.
Technologies: JavaScript, TypeScript, React, Micro frontent, Single-page Applications (SPAs), Sass, Jest, Unit Testing, Testing, CSS, HTML, Confluence, Jira, Deployment, Leadership, Team Mentoring, Code Review, Continuous Improvement, Process Improvement, User Interface (UI), Cloud, Full-stack, CI/CD Pipelines, APIs, Mobile, API Integration, Shadcn, React Query, AI Tools, AI Agents, Application State Management, Google Play Store
HubSpot and Google Cloud Data Integration Specialist
2024 - 2024
BERP LLC
- Developed and implemented a Google Cloud Function to automate data queries and processing, including setting up Service Accounts for secure connections.
- Created and configured a private HubSpot application with authentication to enable API access and securely handle data.
- Integrated and queried 15,000 entries from HubSpot based on specific parameters, including executing complex SQL queries with joins in Google BigQuery.
- Developed an algorithm to process and analyze data, including matching, sorting, and filtering. Ensured efficient interim storage in CSV files for client review and finally writing the processed data back into HubSpot.
- Deployment of the cloud function to the cloud, including comprehensive testing, debugging, and environment setup.
Technologies: HubSpot, Google Cloud, Google BigQuery, Google Cloud Functions, APIs, SQL, REST APIs, REST, Cloud, Authorization, Deployment, RESTFul APIs, Full-stack Development, HubSpot API, Architectural Design, Testing, Unit Testing, Full-stack, CI/CD Pipelines, API Integration
Technical Team Lead
2023 - 2023
Caster
- Led and managed the development team, supporting junior developers and fostering a collaborative work environment.
- Designed and implemented the architecture and functionality for an AI chatbot integrated with OpenAPI.
- Developed a React Native app from scratch for event management and organization and successfully launched it on various app stores.
- Implemented CI/CD pipelines and E2E testing to secure code quality and ensure continuous software delivery.
- Interviewed, evaluated, onboarded, and trained new developers, ensuring they were quickly integrated into their roles and a fit for the organization.
- Conducted regular code reviews to ensure software quality and adherence to best practices.
Technologies: OpenAPI, Amazon Web Services (AWS), Firebase, TypeScript, React Native, Hasura, Bitrise, CI/CD Pipelines, Architecture, Detox, E2E Testing, Scrum, Technical Recruiting, LangChain, Google Cloud Functions, Back-end, Node.js, Google Cloud Platform (GCP), Full-stack, Minimum Viable Product (MVP), HTML5, TypeScript 3, Natural Language Processing (NLP), RESTFul APIs, System Architecture, Full-stack Development, Leadership, User Interface (UI), Fractional CTO, Architectural Design, App Store Deployment, ChatGPT, ChatGPT API, Chatbots, Artificial Intelligence (AI), Large Language Models (LLMs), Team Mentoring, Testing, Unit Testing, Cloud, Android, OpenAI GPT-3 API, OpenAI GPT-4 API, APIs, Mobile Development, Mobile, UX Design, API Integration, AI Agents, App Store, Cross-platform App Development, Google Play Store
Senior Full-stack Developer
2022 - 2022
Caster
- Developed a mobile application in React Native to create, invite, manage, and join certain events.
- Refactored parts of the existing application to decrease code complexity and improve performance.
- Implemented a JWT authentication flow for Firebase Authentication and Hasura.
- Introduced a UI styling system with Storybook, RNUI, and Zeplin.
Technologies: React Native, GraphQL, TypeScript, Hasura, JavaScript, Storybook, PostgreSQL, AWS Lambda, Firebase, Auth0, Zeplin, REST APIs, ECMAScript (ES6), OpenAI GPT-4 API, Android, iOS, Camera API, Google Cloud Functions, Back-end, Node.js, Google Cloud Platform (GCP), Full-stack, Minimum Viable Product (MVP), HTML5, TypeScript 3, Python, Natural Language Processing (NLP), User Experience (UX), RESTFul APIs, System Architecture, Full-stack Development, User Interface (UI), App Store Deployment, OpenAI API, ChatGPT, ChatGPT API, Chatbots, Artificial Intelligence (AI), Large Language Models (LLMs), Testing, Unit Testing, Cloud, CI/CD Pipelines, OpenAI GPT-3 API, APIs, Mobile Development, Mobile, UX Design, API Integration, AI Agents, App Store, Cross-platform App Development, Google Play Store
Front-end Developer
2022 - 2022
Aluma Technologies Ltd.
- Developed a web application from scratch to manage and process intelligent document workflows.
- Integrated PDFTron for previewing, annotating, editing, and navigating PDF documents.
- Implemented a component library with Tailwind CSS.
- Handled the implementation of automated unit and E2E tests using Jest, Testing Library, and Playwright.
Technologies: Svelte, JavaScript, TypeScript, Playwright, Jest, Storybook, PDFTron, PDF, Tailwind CSS, Minimum Viable Product (MVP), HTML5, TypeScript 3, User Experience (UX), RESTFul APIs, Full-stack Development, User Interface (UI), Testing, Unit Testing, CI/CD Pipelines, APIs, API Integration
Software Developer
2020 - 2021
inovex
- Provided development and testing support for a hybrid React Native mobile application in the eHealth space. Refactored the old application and led the transition from JavaScript to TypeScript.
- Developed and tested the React web application for this eHealth product.
- Created the conceptual design and implemented the CI/CD pipeline.
Technologies: TypeScript, JavaScript, React, React Native, Docker, Jest, Git, Codeship, Bitbucket, REST, Xcode, Front-end, Mobile App Development, Software Development, HTML, CSS, Figma, GitHub, Scrum, Visual Studio Code (VS Code), REST APIs, ECMAScript (ES6), Android, iOS, Camera API, Google Cloud Functions, Full-stack, HTML5, TypeScript 3, User Experience (UX), Next.js, RESTFul APIs, Full-stack Development, App Store Deployment, Code Review, Unit Testing, CI/CD Pipelines, APIs, Mobile Development, API Integration, App Store, Expo, Cross-platform App Development, Google Play Store
Front-end Developer
2018 - 2020
Fraunhofer Institute for Manufacturing Engineering and Automation IPA
- Continued development and support of a native Android app with Kotlin to support knowledge management.
- Conceived, planned, and developed a web React application to support the production process and knowledge management.
- Developed a React web application to visualize real-time data in a just-in-time way.
Technologies: React, Redux, OAuth, Git, Docker, Jenkins, REST, Android SDK, Kotlin, Front-end, Mobile App Development, HTML, CSS, React Native, Visual Studio Code (VS Code), iOS, Camera API, HTML5, TypeScript 3, User Experience (UX), RESTFul APIs, Full-stack Development, Leadership, Team Mentoring, CI/CD Pipelines, APIs, Mobile Development, Mobile, API Integration, App Store, Expo, Cross-platform App Development, Google Play Store
Experience
Mymories | An App for Sharing Images Without Losing Data
https://mymories.deA service to share images easily with multiple people at an event without losing data, such as a party, wedding, or holiday. Users can also display live images on a screen. I conceived, designed, and developed the idea from scratch, including the React Native application, the React web front end, and the back end hosted via google cloud functions.
Shuttle Up | An App for Crowdfunding Party Buses
A hybrid app to create and organize crowdfunded bus travels. I developed the app with the Ionic Framework in Angular on the front end, Firebase on the back end, and payment integration via Paypal SDK and Stripe to block and receive payments.
Personal Portfolio Page
A portfolio website with a responsive design optimized for user experience and SEO. Build with React and Next.js for server-side rendering of pages and powerful SEO and responsive TailwindCSS design, including light and dark modes.
STRTax | Tourist Tax Management SaaS
https://strtax.deInvented, planned, and developed STRTax, a multi-tenant SaaS platform for automated tourist tax collection and booking management targeting short-term rental hosts in Germany. Built the full-stack application using Next.js 15 with App Router, TypeScript in strict mode, and Prisma with PostgreSQL.
Implemented a subdomain-based multi-tenancy architecture enabling white-label public check-in pages for each organization alongside a centralized dashboard. Integrated Stripe Connect for payment processing, NextAuth.js for authentication with role-based access control, and external APIs for municipality tax rate synchronization.
Developed automated guest registration workflows, including digital signature capture, document uploads to Amazon S3, and email notifications via Resend. The platform handles complex tax calculations based on guest categories, age groups, and municipality-specific regulations.
Built with shadcn/ui components, full i18n support (German/English), and comprehensive test coverage using Jest and Storybook for visual regression testing.
Implemented a subdomain-based multi-tenancy architecture enabling white-label public check-in pages for each organization alongside a centralized dashboard. Integrated Stripe Connect for payment processing, NextAuth.js for authentication with role-based access control, and external APIs for municipality tax rate synchronization.
Developed automated guest registration workflows, including digital signature capture, document uploads to Amazon S3, and email notifications via Resend. The platform handles complex tax calculations based on guest categories, age groups, and municipality-specific regulations.
Built with shadcn/ui components, full i18n support (German/English), and comprehensive test coverage using Jest and Storybook for visual regression testing.
Education
2015 - 2018
Bachelor's Degree in Business Informatics
Furtwangen University - Furtwangen, Germany
Certifications
JANUARY 2022 - PRESENT
Kubernetes for App Developers (LFD459)
The Linux Foundation
MARCH 2019 - PRESENT
Certified Scrum Master
Scrum Alliance
Skills
Libraries/APIs
React, REST APIs, Node.js, Stripe API, Stripe, Camera API, HubSpot API, React Query, PayPal API, Playwright, OpenAPI, OpenAI API, Auth
Tools
Git, Xcode, GitHub, Shadcn, Claude, Expo, Codeship, Bitbucket, Jenkins, Figma, Adobe Experience Design (XD), Cron, Balsamiq, PDFTron, Auth0, Zeplin, Confluence, Jira, ChatGPT, Prisma
Languages
JavaScript, TypeScript, CSS, HTML, HTML5, TypeScript 3, Python, SQL, ECMAScript (ES6), Java, C++, Kotlin, Bash, GraphQL, Sass
Frameworks
React Native, Redux, Next.js, Jest, Tailwind CSS, Android SDK, Angular, Ionic, Svelte, Detox
Paradigms
REST, Mobile Development, Scrum, UX Design, Model Context Protocol (MCP), E2E Testing, Unit Testing, Testing, Automation
Platforms
Visual Studio Code (VS Code), Firebase, Google Cloud Platform (GCP), Mobile, MacOS, Docker, WordPress, Amazon Web Services (AWS), iOS, HubSpot, Kubernetes, AWS Lambda, Vercel, Bitrise, Android, Cloud Run
Storage
Google Cloud, Databases, MongoDB, Relational Databases, Backblaze B2, Hasura, PostgreSQL
Other
Front-end, Mobile App Development, Software Development, API Integration, CI/CD Pipelines, Full-stack, Minimum Viable Product (MVP), RESTFul APIs, Full-stack Development, App Store, Application State Management, Cross-platform App Development, Google Play Store, OAuth, GitHub Actions, Storybook, MERN Stack, APIs, Google Cloud Functions, Back-end, Google BigQuery, Cloud, Natural Language Processing (NLP), User Experience (UX), FastAPI, Zustand, SaaS Design, System Architecture, Leadership, Large Language Models (LLMs), User Interface (UI), Cursor AI, AI Tools, AI Agents, Networking, Machine Learning, Data Analysis, Prototyping, Certified ScrumMaster (CSM), PDF, OpenAI GPT-3 API, OpenAI GPT-4 API, Architecture, Technical Recruiting, LangChain, HubSpot CRM, Authorization, Deployment, Micro frontent, Single-page Applications (SPAs), Team Mentoring, Code Review, Continuous Improvement, Process Improvement, Retrieval-augmented Generation (RAG), Artificial Intelligence (AI), Chatbots, Portkey.ai, ChatGPT API, App Store Deployment, Architectural Design, CTO, Fractional CTO, Planning, IT Project Management, Multi-tenant SaaS, Multi-tenant Architecture, Software Architecture, Turborepo, Monorepos, Payment APIs, Finance APIs, Row-level Security (RLS), better auth, Authentication
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