Mario Jelinski - Architect / Developer

Q: Where is Mario based?

Mario is based in Berlin, Germany .

Q: What languages does Mario speak?

Mario speaks the following languages: German (Native), English (Advanced) .

Q: How many years of experience does Mario have?

Mario has at least 20 years of experience. During this time, Mario has worked in at least 13 different roles and for 16 different companies . The average length of individual experience is 1 year and 1 month . Note that Mario may not have shared all experience and actually has more experience.

Q: What is Mario's latest experience?

Mario's most recent position is Architect / Developer at handyhase .

Q: What companies has Mario worked for in recent years?

In recent years, Mario has worked for handyhase , epostbox / compador , Organ Printing - CNC Modification/Expansion , Axel Springer SE - upday GmbH , and rapid-data .

Q: Which industries is Mario most experienced in?

Mario is most experienced in industries like Information Technology (IT) , Government and Public Administration , and Retail . Mario also has some experience in Energy , Manufacturing , and Biotechnology .

Q: Which business areas is Mario most experienced in?

Mario is most experienced in business areas like Information Technology (IT) , Product Development , and Marketing . Mario also has some experience in Quality Assurance (QA) and Human Resources (HR) .

Q: Which industries has Mario worked in recently?

Mario has recently worked in industries like Information Technology (IT) , Biotechnology , Media, and Entertainment and Publishing .

Q: Which business areas has Mario worked in recently?

Mario has recently worked in business areas like Information Technology (IT) , Product Development , and Quality Assurance (QA) .

Recommended expert

Berlin, Germany

Experience

Feb 2025 - Apr 2025

3 months

Architect / Developer

handyhase

Overhaul of the entire design and implementation of new UI/UX aspects using React
Planning of the software architecture and structuring of the project for long-term scalability using Git for version control

Dec 2024 - Jan 2025

2 months

Mobile Testing & Debugging

Developed and maintained automated test scripts for UI and functionality testing using Firebase Test Lab
Integrated automated testing into CI/CD pipeline using Git

Apr 2023 - Feb 2024

11 months

Developer

epostbox / compador

Optimized digital mail services including printing, PDF conversion, text recognition, and digital signatures
Developed a Vue-based training system for accurate address recognition using GPT-4All and proprietary AI models
Developed a 5-factor login and authentication system with FIDO2 for secure, passwordless authentication
Managed cron jobs with PHP, Node.js, and Java
Implemented GraphQL for optimized data queries and comprehensive log analyses
Managed SFTP processes in PHP for efficient and secure data exchange
Managed ADFS servers and SAML 2.0 and set up internal Git systems with Gitea and pipeline automation

Jan 2023 - Aug 2024

1 year 8 months

Developer

Organ Printing - CNC Modification/Expansion

Ported GBRLHal to a 32-bit STM32 microcontroller for enhanced 3D printing capabilities
Created a QT QML-based configuration and monitoring interface

Apr 2022 - Dec 2022

9 months

Frontend Developer

Axel Springer SE - upday GmbH

Redeveloped the Article Importer app using React and REST API
Created a soccer app for the 2022 World Cup featuring events, lineups, statistics, and knockout phase information with extensive testing across mobile devices using Firebase Labs
Established robust testing pipelines and Git release pipelines
Migrated React-based projects to Angular and Vue

Jan 2022 - Apr 2022

4 months

Fullstack Developer

rapid-data

Implemented micro-frontends using Storybook and React
Worked with REST APIs, Redux, Recoil, and React-hook-form for efficient data handling
Used JUnit and modern CI pipelines for quality assurance
Managed codebase with Git and implemented release pipelines

May 2020 - Dec 2021

1 year 8 months

Software Developer / Lead

Auconet GmbH

Managed large data imports (SAP, Loga, CSV, XML) into dynamic databases for validation and transformation
Rebuilt a legacy Java-based platform to React
Automated builds and deployments with Maven and Ant
Ensured code quality with JUnit and CI pipelines
Maintained code quality and collaboration with Git

Dec 2019 - Apr 2020

5 months

Senior Software Developer

Dive-solutions

Built interactive 3D visualizations for fluid simulations using React and Three.js
Created scalable, responsive web applications using React and Redux

Nov 2018 - Nov 2019

1 year 1 month

Senior Developer

Cyren GmbH

Developed backend solutions for email spam detection using Java and Spring Boot and tested with JUnit
Enhanced the Pluto Customer Configuration Platform with React
Collaborated using Git for version control

Apr 2016 - Oct 2018

2 years 7 months

Software Developer

Strato AG / 1&1 / IONOS

Built and maintained customer platforms including Strato Customer Login, Server Login, and the IONOS product page using Django, JavaScript, and Python
Designed responsive UIs with React, Vue, Angular, and Bootstrap
Implemented OAuth 2 and Single Sign-On for secure user authentication
Improved page speed from 7 seconds to under 950ms
Implemented protections against XSS and conducted A/B and Multi-Armed Bandit tests
Worked on server cloud solutions with Java and OpenStack

Oct 2013 - Mar 2016

2 years 6 months

Software Developer

eBay

Developed and maintained backend and frontend features for Loquo and Alamaula using Java, JavaScript, PHP, Smarty, and CakePHP
Conducted SEO optimization and created sandbox environments for SEO testing
Implemented error tracking and redirect management using Grafana
Optimized search functionality with Elastic Search and managed large-scale data imports for search pages
Built responsive interfaces using Prototype and jQuery and optimized page performance
Maintained systems on OpenStack with monitoring via Grafana

Apr 2011 - Sep 2013

2 years 6 months

Software Developer

dooyoo (Leguide / Lagardere)

Built and enhanced a price comparison platform focusing on scalability and performance
Developed CPC calculation and invoicing systems
Optimized platform for search engines to improve visibility and traffic
Implemented vector-based data mapping for efficient offer matching
Designed a custom MVC framework for the platform
Analyzed traffic and tracked outgoing clicks for accurate invoicing

Jan 2008 - Dec 2010

3 years

Software Developer

Bardenheuer (Bundesdruckerei)

Developed image recognition and processing software for ePass Readers using C, C++, Halcon, Boost, and Qt
Created a calibration tool for ePass Readers
Collaborated on specifications and performed requirements analysis using UML
Developed a PHP-based project management tool to support internal workflows

Jan 2008 - Dec 2008

1 year

Game Developer

LBXGames

Created Nintendo DS game mechanics using Assembler, C, and C++
Designed and implemented game logic with a custom scripting language
Built level editors in C# to streamline game design processes

Jan 2008 - Dec 2008

1 year

Developer

NetworkedAssets

Contributed to cable modem design using Java and Perl
Conducted performance and stress tests on cable networks

Jan 2007 - Dec 2007

1 year

Working student - IT-Helpdesk

Siemens PG Huttenstraße Gasturbinenwerk Berlin

Managed and maintained network infrastructure
Configured and deployed hardware and software
Conducted monitoring and measurement activities for gas turbines

Jan 2006 - Dec 2006

1 year

Developer / Administration

Siemens PG Huttenstraße Gasturbinenwerk Berlin

Developed ERA employee management software

Jan 2005 - Dec 2005

1 year

Student

Charité Berlin / TFH Berlin

Developed a smartcard login system for hospitals

Industries Experience

See where this freelancer has spent most of their professional time. Longer bars indicate deeper hands-on experience, while shorter ones reflect targeted or project-based work.

Experienced in Information Technology (13 years), Government and Administration (3 years), Retail (2.5 years), Energy (2 years), Manufacturing (2 years), and Biotechnology (1.5 years).

Information Technology

Government and Administration

Retail

Energy

Manufacturing

Biotechnology

Business Areas Experience

The graph below provides a cumulative view of the freelancer's experience across multiple business areas, calculated from completed and active engagements. It highlights the areas where the freelancer has most frequently contributed to planning, execution, and delivery of business outcomes.

Experienced in Information Technology (19.5 years), Product Development (12.5 years), Marketing (2.5 years), Quality Assurance (2 years), and Human Resources (1 year).

Information Technology

Product Development

Marketing

Quality Assurance

Human Resources

Summary

Experienced Software Engineer with a strong focus on Java, Spring Boot, Maven, Ant, Git, React, and Angular. Proven track record in designing and implementing scalable backend and frontend solutions, optimizing build and deployment pipelines, and ensuring high code quality with JUnit and modern CI/CD practices. Adept at collaborating in agile teams and delivering robust software under tight deadlines.

Skills

Core Technologies

Java > 10 Years
Spring Boot > 6 Years
Maven > 8 Years
Ant > 7 Years
Junit > 8 Years
Git > 10 Years
React > 6 Years
Angular > 6 Years

Programming Languages & Frameworks

Javascript > 10 Years
Java > 10 Years
C++ > 5 Years
Php > 8 Years
Python > 6 Years
React > 5 Years
Vue > 4 Years
Angular > 5 Years
Node.js > 6 Years
Kotlin > 3 Years
Spring Boot > 5 Years
Hibernate > 5 Years
Typescript > 5 Years
Three.js > 4 Years
Phaser > 3 Years

Web-server And Infrastructur

Apache > 8 Years
Nginx > 6 Years
Docker > 6 Years
Kubernetes > 4 Years
Aws > 6 Years

Monitoring And Performance-tools

Grafana > 5 Years
Prometheus > 4 Years
New Relic > 3 Years
Datadog > 4 Years

Authentication & Security

Oauth2 / Openid Connect > 6 Years
Jwt (Json Web Token) > 5 Years
Single Sign-on (Sso) > 5 Years

Databases

Mysql > 10 Years
Postgresql > 8 Years
Mongodb > 6 Years

Version Control & Project Management

Git > 10 Years
Jira > 8 Years
Asana > 5 Years

Testing

Unit Testing (Jest, Junit, Pytest, Etc.) > 8 Years
Integration Testing > 6 Years
End-to-end Testing (Cypress, Selenium) > 5 Years
Test Automation / Ci Pipelines > 6 Years

Languages

German

Native

English

Advanced

Education

Oct 2008 - Jun 2010

Beuth University of Applied Sciences Berlin

Master of Engineering · Embedded Systems · Berlin, Germany

Oct 2003 - Jun 2007

Technical University of Applied Sciences Berlin

Diploma Engineer · Technical Computer Science Real-Time Systems · Berlin, Germany

Oct 2000 - Jun 2003

Lette Association (Public Law Foundation)

State-Certified Assistant for Electronics and Data Technology · Electronics and Data Technology · Berlin, Germany

Profile

Created

August 2025

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Frequently asked questions

Do you have questions? Here you can find further information.

Where is Mario based?

Mario is based in Berlin, Germany.

What languages does Mario speak?

Mario speaks the following languages: German (Native), English (Advanced).

How many years of experience does Mario have?

Mario has at least 20 years of experience. During this time, Mario has worked in at least 13 different roles and for 16 different companies. The average length of individual experience is 1 year and 1 month. Note that Mario may not have shared all experience and actually has more experience.

What roles would Mario be best suited for?

Based on recent experience, Mario would be well-suited for roles such as: Architect / Developer, Mobile Testing & Debugging, Developer.

What is Mario's latest experience?

Mario's most recent position is Architect / Developer at handyhase.

What companies has Mario worked for in recent years?

In recent years, Mario has worked for handyhase, epostbox / compador, Organ Printing - CNC Modification/Expansion, Axel Springer SE - upday GmbH, and rapid-data.

Which industries is Mario most experienced in?

Mario is most experienced in industries like Information Technology (IT), Government and Public Administration, and Retail. Mario also has some experience in Energy, Manufacturing, and Biotechnology.

Which business areas is Mario most experienced in?

Mario is most experienced in business areas like Information Technology (IT), Product Development, and Marketing. Mario also has some experience in Quality Assurance (QA) and Human Resources (HR).

Which industries has Mario worked in recently?

Mario has recently worked in industries like Information Technology (IT), Biotechnology, Media, and Entertainment and Publishing.

Which business areas has Mario worked in recently?

Mario has recently worked in business areas like Information Technology (IT), Product Development, and Quality Assurance (QA).

What is Mario's education?

Mario holds a Master in Embedded Systems from Beuth University of Applied Sciences Berlin and a Bachelor in Technical Computer Science Real-Time Systems from Technical University of Applied Sciences Berlin.

What is the availability of Mario?

Mario is immediately available full-time for suitable projects.

What is the rate of Mario?

Mario's rate depends on the specific project requirements. Please use the Meet button on the profile to schedule a meeting and discuss the details.