Sergkei Kournosenkov
Web & Software Developer · Full-Stack · Frontend focus · Wuppertal, Germany
Experienced Full-Stack Software Engineer with a strong focus on frontend development and modern web applications. Proven track record of leading technical teams, building dynamic single-page applications (SPAs), and integrating AI-powered development tools. Passionate about clean code, performance optimization, and scalable architectures.
ser.corum@gmail.com · GitHub · LinkedIn
Professional experience
Software Engineer – Full-Stack (Frontend Focus), ECS GmbH
04/2019 – present
- New development and maintenance of complex single-page applications (SPA) using Angular (React, Flutter).
- Implementation of responsive designs with HTML5, SASS/LESS and Bootstrap/Tailwind to ensure optimal UX on all devices.
- Connection of RESTful APIs to the frontend and close cooperation with the backend team (e.g. Java Spring Boot).
- Optimize application performance and ensure cross-browser compatibility.
- Analysis and performance optimization of complex SQL queries (MySQL/PostgreSQL) to reduce loading times in data-intensive applications
- Develop low-code solutions using the Mendix platform to quickly deploy business apps.
- Ensuring high code quality and maintainability through the establishment of clean code guidelines and static code analysis (SonarQube, ESLint, Prettier).
- AI-powered software development with Agentic Coding (Claude Code, Github Copilot, Gemini/Anti-gravity)
- Design and implementation of automated unit tests (Karma/Jasmine, Vitest) to increase test coverage and avoid regressions.
- Conducting regular code reviews for quality assurance and knowledge exchange within the team.
- Expert advice to project management and stakeholders on the selection of technologies and architectural decisions.
- Actively promote a collaborative developer culture and guide junior developers on complex problems.
Technologies: Angular, React, Flutter, Tailwind, Spring Boot, PostgreSQL, Mendix, Vitest, Claude Code
Web Software Developer and Head of IT, Nonomella GmbH
04/2017 – 03/2019
- Technical management of the IT department as well as coordination of internal and external development resources.
- Support and further development of the e-commerce landscape (e.g. JTL Shop & JTL Wawi) as well as interface management.
- Planning and implementation of the IT infrastructure strategy to support the operational business.
- Full-stack development of features for the webshop using PHP and MySQL.
Technologies: PHP, MySQL, JTL Shop, JTL Wawi, IT Strategy
Web and Software Developer, Koszewa & Koszewa GbR
11/2014 – 03/2017
- Conception and implementation of dynamic websites and applications with jQuery, Bootstrap, HTML, PHP, MySQL and C#.
- Development and maintenance of internal management systems for the automation of business processes.
- Design and implementation of relational database structures and complex SQL queries.
- Second-level support and error analysis for existing software solutions.
Technologies: jQuery, Bootstrap, PHP, MySQL, C#
Technical Support Staff, Refuel / InSpot · Ioannina, Greece
2006 – 2011
- Provided technical support and troubleshooting for internet cafe systems.
Technologies: Support, Troubleshooting
Selected projects
Energy sector: streamlined bid management system
ECS GmbH · energy sector client · 2021 – 2026
Built core features (complex, adjustable questionnaire templates, versioning, sync between multiple external systems) that automate and accelerate the bid process, and led the migration from Angular 15 to 22 while development continued.
nonomo.de: from intern to shop relaunch
Nonomella GmbH · nonomo.de · 2016 – 2019
Three stages: started as an intern, led frontend and backend on the first upgrade, then the full overhaul with a custom configurator and a modern, responsive design.
fidella.org: purchase advisor & modernisation
Nonomella GmbH · fidella.org · 2016 – 2019
Built an interactive purchase advisor and modernised the shop.
Portfolio: all projects
Skills
- Frontend & UI: Angular, JavaScript, HTML5, CSS / SCSS, React, Tailwind, Bootstrap, SASS / LESS, Flutter / Dart, jQuery, Ajax, ExtJS3
- Backend & Languages: Java Spring Boot, PHP (OOP), Smarty 2/3/4, C#, Objective C, Matlab
- Databases: MySQL, PostgreSQL, SQL Server (T-SQL)
- APIs & Architecture: RESTful APIs, SOAP APIs, Facebook & Instagram APIs, Google Platforms & APIs
- Quality & Testing: SonarQube, ESLint, Karma / Jasmine, Vitest, Prettier
- AI Tooling: Claude Code, GitHub Copilot, Gemini / Anti-gravity
- DevOps & VCS: GitHub, GitLab, Gitea, Subversion
- Platforms & Tools: Mendix (Low-code), Jira, Confluence, Agile / Scrum, JTL Shop, JTL Wawi, SAP, Salesforce, MS Office, Adobe Photoshop
Education
- B.Sc. in Computer Engineering (Software Engineering), Technological Educational Institute of Epirus (2008 – 2015)
- Vocational Training (Telecommunications & Networks), Vocational Training Institute, Ioannina, Greece (2006 – 2007)
- European Computer Driving Licence (ECDL), Athens (2006)
- High School Diploma, Greek Lyceum Nuremberg (2004)
Languages
- Greek: Native
- English: C1 · Fluent
- German: B2 · Very good
- Russian: Very good
English · Deutsch · Ελληνικά
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