Jonatan Fekete, Developer in Barcelona, Spain
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Jonatan Fekete

Verified Expert  in Engineering

Full-stack Developer

Barcelona, Spain
Toptal Member Since
March 19, 2018

Johnny is a full-stack developer who specializes in building customer-facing web applications and business systems. He has more than a decade of experience in architecture design, PHP development, database engineering, and web-based front-end technologies. Johnny joined Toptal to find fresh companies with a growth mindset where original ideas are acknowledged and where he could contribute to the final product.


Wellet Corp.
React, React Native, Redux
Love Worldwide
React Native, Animation, React Redux, Node.js, AdonisJS
Volta Technologies
React Native, React, Redux, React Redux, Swift




Preferred Environment

React, Laravel, Webpack, NPM, Visual Studio Code (VS Code), Continuous Integration (CI)

The most amazing...

...project I've worked on was an applicant-tracking system that I designed and built from scratch and led it to success.

Work Experience

Full-stack developer

2021 - 2022
Wellet Corp.
  • Worked on various platforms of an event ticketing system.
  • Improved the legacy codebase of the web-based sales system.
  • Implemented modern build flows, and upgraded libraries to the latest versions, while adding new functionalities to work with multiple API endpoints and payment solutions.
  • Made a React Native mobile app to facilitate sales.
  • Created a React Native app to enable scanning and validating tickets and manage reseller commissions.
Technologies: React, React Native, Redux

Mobile app developer

2020 - 2021
Love Worldwide
  • Made a fully functional MVP for a dating app in React Native, with a Node.js back end.
  • Created the designs, architecture, and code of all of the basic functionalities based on descriptions from the client.
  • Implemented complex animations, as it was one of the primary differentiators of the app.
Technologies: React Native, Animation, React Redux, Node.js, AdonisJS

Mobile app developer

2020 - 2020
Volta Technologies
  • Developed a react native app that supports saliva-based PCR testing.
  • Worked together with the team to submit a COVID-related health app to App Store and Android Play Store.
  • Followed quick development cycles as it was a very urgent, time-sensitive project.
  • Integrated third-party APIs to address validation, QR reader.
Technologies: React Native, React, Redux, React Redux, Swift

Full-stack Laravel Developer

2020 - 2020
  • Worked on a learning platform for educating children about finance. Created the PHP back end using Laravel with API endpoints, authentication, authorization, and testing, while ensuring it can handle many requests and respond quickly.
  • Contributed to the platform's front end built-in Vue.js by following the best practices and connecting it to the Laravel back end.
  • Created a custom video player and rich content for custom tests so the material can be presented entertainingly.
Technologies: Laravel, PHP 7, E2E Testing, Unit Testing, Vue, APIs, REST APIs

Full-stack JavaScript Developer

2018 - 2019
  • Created a React-based web app from scratch and followed the provided designs.
  • Designed the database, system architecture, models, and relations.
  • Built the data-heavy back end in Node.js with AdonisJs, following the framework's best practices (about architecture, events, authentication).
  • Connected to multiple APIs to retrieve massive amounts of financial and statistical data.
  • Created complex data visualizations with D3.js.
Technologies: MySQL, AdonisJS, D3.js, ECMAScript (ES6), Redux, React, Node.js

Full-stack Developer

2018 - 2018
  • Created from scratch a React-based web app that followed the provided designs.
  • Designed the database, system architecture, models and relations.
  • Built the back end in Laravel, following the framework's best practices (about architecture, events, notifications).
  • Connected to multiple APIs (Google APIs, Stripe payment integration, Twilio, and SendGrid).
  • Set up Elasticsearch and Redis and optimized the system's performance.
  • Configured continuous integration, deployment, and scalable development processes.
Technologies: Git, Continuous Integration (CI), DigitalOcean, Docker, Jest, Redis, Redux, Elasticsearch, MySQL, Laravel, ECMAScript (ES6), React

Full-stack Developer | Co-founder

2016 - 2018
  • Created an online applicant tracking system from scratch.
  • Converted the business concepts and processes into architectural plans and developed a user-friendly online application.
  • Used Laravel as a back-end framework with multiple integrations including Elasticsearch, a Word-to-PDF conversion, and third-party APIs.
  • Developed a responsive, highly interactive front end.
  • Configured the underlying server architecture, managed the development, and implemented continuous integration environment.
  • Wrote unit and end-to-end tests, scaled the system, and constantly improved the stability of the product.
  • Managed the underlying server architecture (AWS and later Digital Ocean).
Technologies: Amazon Web Services (AWS), Git, Sass, React, jQuery, JavaScript, Elasticsearch, Laravel, PHP

Full-stack Developer

2016 - 2017
Starfly Media ApS
  • Developed the server-side web application logic and integrated an internally used system.
  • Connected a Symfony application to numerous APIs and automated the processing of massive amounts of data.
  • Implemented various optimization caching techniques to enable a high performance.
  • Added visual interfaces to provide an overview of the running processes and created statistic dashboards to give real-time insights.
Technologies: jQuery, JavaScript, HTML5, Symfony, PHP

Back-end Developer

2016 - 2016
Elements Interactive
  • Collaborated with cross-functional teams to design and implement new features and services to support our client applications.
  • Created a back-end and REST API for a mobile platform.
  • Modernized an existing PHP application and implemented Elasticsearch.
  • Introduced new functionalities that were supported by unit tests using PHPUnit and Composer.
Technologies: Git, jQuery, JavaScript, HTML5, Elasticsearch, MySQL, Django, Python, Laravel, PHP

Full-stack Developer

2015 - 2016
  • Worked on multiple marketing-driven projects with a very short turnaround in a fast-paced digital agency.
  • Created numerous online games and websites.
  • Customized WordPress to satisfy client needs; optimized them to stay fast and functional even with high traffic.
  • Integrated various third-party APIs for data visualization and social media statistics.
Technologies: Git, MySQL, jQuery, JavaScript, HTML5, WordPress, PHP

Full-stack Developer

2012 - 2015
  • Designed and developed the front end of a business process management system.
  • Worked extensively on the front end doing everything from designing the user interfaces to creating the HTML and CSS and adding a rich user interaction.
  • Integrated different APIs and libraries while making sure that the client-server communication is seamless.
  • Wrote PHP scripts to facilitate the development of the application.
  • Managed the AWS setup of the system.
Technologies: Amazon Web Services (AWS), Backbone.js, jQuery, JavaScript, CSS, HTML5, MySQL, PHP

Web Application Engineer

2011 - 2012
InvenQ Insight
  • Worked on a cloud-based business process modeling system.
  • Designed and developed the platform from scratch, using various server- and client-side technologies.
  • Implemented custom HTML canvas functionalities for working with flow models.
Technologies: Git, CSS, HTML5, jQuery, JavaScript, MySQL, PHP

Lead Web Developer

2011 - 2012
Pegasus Online Media
  • Planned, designed, and developed a vertical price comparison site.
  • Consolidated numerous webshops' product catalogs through APIs.
  • Integrated a social network functionality to the existing sites, maximized the search engine optimization, and worked with data security.
Technologies: CSS3, HTML5, jQuery, JavaScript, MySQL, PHP

Software Developer

2007 - 2011
Jonatan Fekete e-Solutions
  • Created numerous websites and web shops.
  • Customized WordPress and its plugins to achieve specific client requirements.
Technologies: Amazon Web Services (AWS), jQuery, JavaScript, CSS, HTML5, MySQL, PHP

User Onboarding and Product Tour Creator
Bonboarding is a tool designed to help digital products offer better user onboarding experiences by enabling them to add in-app product tours, highlight elements, and add popups that seamlessly match their design. All this is in a no-code solution that functions as a layer on top of the web app.

There were many challenges during this project, such as creating a Chrome extension integrating with any underlying app that might use various front-end technologies.

React Native Application for Retail Employees
As a CTO and lead developer, I worked in a Barcelona-based startup, Beam HR. Our application is used by the employees of various retails stores in Spain to view their schedules, request holidays and changes, notify their managers of sick leaves or chat with coworkers.

The application communicates with different back-end APIs and uses technologies such as notifications, GPS, or local database.

As a developer, I worked on both the back- and front-end side of the project, while simultaneously focusing on optimization, easy-to-use UI interfaces, error-proof infrastructure, and writing clean code.

Recruitio is a digital talent sourcing tool that improves the process of finding the best candidates for your job openings.

As a technical co-founder, I built the whole system from scratch, made all initial technological and architectural decisions, chose the back-end and front-end technologies, and implemented the system through an agile development process. The system was integrated with various external services, and I implemented an assortment of features such as Elasticsearch or Word-to-PDF conversion.

After our user base started increasing, I ensured that the system could scale and function smoothly while always protecting sensitive client data. I introduced continuous integration, efficient development, and deployment processes.

Back End for a Location-tracking Mobile App

I worked with a team at Elements Interactive to build a location-tracking application to prevent young people from using their phones while riding.

I developed the admin interface and the REST API that served hundreds of users simultaneously at peak periods. I also implemented the testing and access management with multi-level user roles.

Weekly Meal Planner

As part of Isobar, I worked on a project for one of Denmark's largest grocery stores. The web app consisted of hundreds of meal recipes and let users mix and match them to plan ahead for their week, generating a consolidated shopping list at the end.

Although the project was part of a WordPress environment, I developed many custom functionalities in PHP and JavaScript.

Mentoring Others in Code
I believe that it's never too late to learn to code, and in the previous years, I organized many free web and PHP introduction courses—helping more than a hundred people in total.

Besides that, I mentored several beginners and helped them get their first developer jobs. I also organized some small hackathons to motivate them and show how much can be achieved within just a weekend.

Pruexx | An Online Business Process Modeling System

I created a web app at the dawn of HTML5 Canvas so I had to write custom functionalities in order for users to be able to drag and drop elements, connect them, edit properties, and format.

I used JavaScript, jQuery, and many libraries to achieve smooth user experiences while the back-end ran on PHP with MySQL.
2012 - 2016

Master's Degree in Business Administration and Information Systems

Copenhagen Business School - Copenhagen, Denmark

2007 - 2011

Bachelor's Degree in Business Information Systems

Corvinus University of Budapest - Budapest, Hungary


jQuery, jQuery UI, React, Node.js, Facebook API, FPDF, Google Maps, D3.js, REST APIs, Backbone.js, Vue, React Redux


GitHub, Sublime Text 3, Git, Trello, Xcode, wkhtmltopdf, Sketch, Photoshop CC, Illustrator CC, NGINX, Composer, Sublime Text, Interface Builder, Webpack, NPM, Jira


Laravel, React Native, Laravel 5, Symfony 3, Symfony, Redux, OAuth 2, PHPUnit, AdonisJS, Django, Jest


CSS, CSS3, JavaScript, PHP 7, JavaScript 6, PHP, SQL, TypeScript, Sass, HTML5, Python, ECMAScript (ES6), Objective-C, Swift, Python 3, GraphQL


REST, Scrum, Agile, Kanban, E2E Testing, Continuous Integration (CI), Unit Testing


WordPress, Visual Studio Code (VS Code), Firebase, iOS, Linux, Ubuntu, Amazon EC2, Unix, Apache2, MacOS, DigitalOcean, Amazon Web Services (AWS), Docker


Elasticsearch, MySQL, Amazon S3 (AWS S3), MongoDB, NoSQL, Redis


GitFlow, Ajax, Axios, OOP Designs, App UX, WordPress Plugins, WordPress Themes, SaaS, Web App Development, Back-end, Front-end, APIs, Animation, Chrome Extensions, Firefox Extensions

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