Full Stack Developers in Cologne

• SPA for automated communication of medical findings with role-based access (Sanctum)
• Server-side LLM integration (OpenRouter) with structured processing
• Automated sending via SMS/voice call (Twilio, ElevenLabs) with queue + status retry
• Full test coverage with 80+ documented test cases

Technologies: PHP, Laravel, LLM API (OpenRouter), Twilio, ElevenLabs, Laravel Sanctum, PHPUnit, Playwright, Docker, REST

PLANT-MY-TREE®-per-order

The application enables Shopify merchants to automatically place tree-planting orders for every incoming order. By integrating ecological contributions directly into the purchase process, the manual effort for tracking and billing reforestation initiatives is eliminated. The system increases transparency for end customers through real-time visualizations of the ecological impact directly in the storefront. The architecture is based on a modular monolith with Spring Boot in the backend and an integrated React app inside the Shopify admin area. The solution uses webhooks to capture order data in an event-driven way and integrates the weclapp ERP system for automated monthly invoicing. An app proxy mechanism provides dynamic statistics such as CO2 compensation and planted trees without any performance loss for the merchant shop.

Tasks:

• Design of the modular software architecture based on Spring Modulith to ensure high maintainability
• Development of the event-driven business logic for evaluating Shopify orders via webhooks
• Implementation of automated invoicing by connecting the weclapp REST API
• Building the frontend using React Router and Shopify App Bridge for native integration
• Design of the database model and implementation of the persistence layer with JPA/Hibernate and Prisma
• Integration of internationalization processes for global use in the frontend and email communication
• Automation of deployment processes using Docker and GitLab CI/CD

Project skills: Java 25, Spring Boot, Spring Security, Spring Modulith, Hibernate, JPA, REST API, PostgreSQL, Maven, Liquibase, React, TypeScript, React Router, Vite, Node.js, Prisma, Zod, Docker, Docker Compose, GitLab CI/CD, Shopify CLI, Shopify App Bridge, Polaris, weclapp, i18next, Lombok, Vitest

• Built more than 15 frontend applications and more than 10 backend services across internal tools, back-office workflows, and external portals for installers and end customers
• Automate build and release workflows with TypeScript and Azure DevOps
• Mentor junior engineers through code reviews and technical guidance
• Integrate AI-assisted and agentic development practices into engineering workflows
• Coordinate user experience decisions with UX designers

Tech Stack: Claude Code, Codex, AWS (S3, Lambda, AppSync, Resolver), Next.js App Router, ReactJS, NuxtJS, Vue.js, Storybook, JavaScript, TypeScript, GraphQL, Azure DevOps

• Further development of a policy administration system (contract/claims) for the legal expenses insurer ÖRAG.
• My role: Senior Software Developer.
• The team consists of 12 developers.
• Technologies used: Java 8/21, Java EE, Quarkus, WebLogic, JPA, RabbitMQ, JTA, CI, CD, Jenkins, DB2, Maven, Jenkins, GIT (bitbucket) later GitLab, Junit, Elasticsearch, Mockito, Jira, SonarQube, Scrum, React, Workflow
• Migration and modernization of legacy systems: rewrote C and C++ code in Java to improve maintainability, scalability, and performance. Refactored Python into Java, including optimization and integration into modern architectures.
• Study on the use of AI (Codex) for implementing a Java feature. The goal is to compare the time spent and productivity of AI-supported development with a classic implementation by a developer. The results should show how strongly the use of AI affects development time and efficiency.
• Development of the following tariff calculators for the years 2024/2026: private, companies, doctors, farmers, owner-occupied G + H, landlords, traffic, club, top managers, sales representatives, special criminal law, savings bank, municipal, BayGT, doctors, Dehoga

PFS-Matching-App

• Integrated an intelligent LLM chatbot using LangChain4j, enabling conversational AI, context-aware question answering, document summarization, and autonomous tool execution.
• Implemented Retrieval-Augmented Generation (RAG), prompt engineering, and AI agent workflows to connect large language models with enterprise data and backend services.
• Developed RESTful APIs and secure backend services to support AI-driven interactions and business processes

• A warehouse valuation system was reimplemented using Java, Spring Boot, and Camunda. The backend solution focuses on integration and batch calculations, the frontend on managing formulas and reviewing results.
• Java 21
• Spring Boot
• JPA
• Maven
• REST
• Kafka
• PostgreSQL
• DB2
• Liquibase
• Google Cloud Storage
• Keycloak
• GitLab CI/CD
• Helm
• Terragrunt
• SonarQube
• Angular
• IntelliJ
• JUnit 5
• Mockito
• Open API

• Two-month modernization of the management UI for AI-powered cameras
• Rewrote a complex React application to Vue 3 with single file components
• Set up the core architecture of the Vue application and configured Vite, Pinia, Router, I18n, ESLint, and Prettier
• Custom integration of Leaflet to display detection zones on images
• Assisted with backend extension and authentication adjustments

• Develop powerful add-ons for customer service systems with innovative Zendesk apps designed to drive business growth, improve efficiency, and enhance customer satisfaction
• Implement full Zendesk solutions and provide hands-on support to bring customer service vision to life
• Combine customer service and technology expertise to address the complexities of delivering top-notch customer service
• Execute Zendesk implementations in 20+ countries and develop AI apps that automate replies
• Maintain a proven track record of success in advancing customer service capabilities

• Development of an app
• Technologies: React Native, Expo, SupaBase, TypeScript, GitHub, Trello

• Development of monitoring and control systems for public transport
• Development of a platform for real-time monitoring of passenger information and ticketing systems and an application for remote control and status monitoring of access systems
• Development of dynamic forms, complex tables, real-time dashboards (SignalR), and reusable components in the frontend (using Storybook)
• Implementation of REST interfaces in the backend
• Deployment to Microsoft Azure Cloud
• Technologies used: Angular 20, Angular Material 3, Dev Extreme, Storybook, C#/.NET 10

• Typoscript
• Extbase
• Fluid
• Typescript
• requireJS
• WebVital

• Design, development, and monitoring of microservices
• Migrating functions from a monolithic system into separate microservices
• Designing and implementing new microservices (backend and frontend)
• Setting up and maintaining a CI/CD pipeline (GitHub Actions)
• Configuring cloud infrastructure with AWS CDK and Terraform
• Designing and implementing event-driven communication with AWS SNS/SQS and Apache Kafka
• Ensuring code quality through Test Driven Development (TDD), static code analysis, and Clean Code