Mario Slepcevic, Full-stack Web Developer in Zagreb, Croatia
Mario Slepcevic

Full-stack Web Developer in Zagreb, Croatia

Member since July 15, 2020
Mario is a full-stack web developer with more than eight years of overall programming experience. On whatever project Mario works on, he strives to keep his code simple and well tested. When working for clients, Mario likes using stable and proven tools but is fearless when digging into bleeding-edge technologies to keep things fresh.
Mario is now available for hire


  • Pinkdroids
    Notion, Figma, Slack, GitHub, Docker, Gatsby, Next.js, React, JavaScript...
  • Partner Banka
    Backbone.js, JavaScript, Flask, Python



Zagreb, Croatia



Preferred Environment

Google Chrome, ITerm, Visual Studio Code, Slack, MacOS

The most amazing...

...thing I've developed was an API for a sports app which provided live results for matches that couldn't be seen anywhere else and included the national league.


  • Mid and Senior Full-stack Developer

    2017 - PRESENT
    • Worked as part of a team that worked on a government web app with a high user load that demanded adherence to strict accessibility standards while also providing content in multiple languages which included some that were written right to left.
    • Developed a couple of projects for a big real-estate company including building a website using Next.js in conjunction with Contentful, and creating a couple of web apps using GraphQL that were used to manage real estate-related resources.
    • Developed a hospitality web application for an exclusive member's club. The back end had an admin interface used for data entry and creation of the front-end part of the site itself but also an API used by the front end for user actions.
    • Wrote code that was highly tested for each project and wrote the tests myself including back-end tests (mostly unit tests) and front-end tests (unit and integration tests).
    • Composed, for certain projects. E2E tests using Cypress and quality assurance tests using Lighthouse.
    • Developed the company's website using Gatsby and Contentful while actively taking part in creating the site's content by writing blog posts.
    • Contributed to the build of the company's internal dashboard app which, alongside a lot of administrative functionality, included a custom time-tracking feature for employees.
    Technologies: Notion, Figma, Slack, GitHub, Docker, Gatsby, Next.js, React, JavaScript, Django, Python
  • Junior and Mid Full-stack Developer

    2014 - 2017
    Partner Banka
    • Developed multiple web apps used by bank employees for internal processes. Most of the apps were in communication through their respective APIs and all of the apps used a custom single-sign-on implementation.
    • Developed an API for sending SMS notifications with a front end where all the messages could be viewed/sent in the form of chats.
    • Built and maintained a network of sensory systems (temperature, moisture, and so on) that were needed to send notifications if certain thresholds were surpassed. The system used the mentioned SMS app to send alarm messages.
    • Made a radio web app for employees that used a backend that accumulated and provided different local online radio streams through a simple interface. It also scraped and showed what was currently playing when the data was available.
    • Built a static web app to show the current exchange rates on big screens in the bank's branches across the country. It was mostly viewed by customers, so it needed to always be fullscreen and have a seamless startup if power was lost.
    Technologies: Backbone.js, JavaScript, Flask, Python


  • Hospitality Web Application for a San Francisco-based Member's Club

    I worked on both the front end and back end in a small team scattered around Europe and the US. The back end was built to be used directly from an admin interface, as well as an API. It included a custom site builder interface that could be used by administrators to customize the look and feel of the front end. The API was used from the front end, mostly for user actions, but it was built also to be used by external resources. The code was thoroughly tested on both the frontend and the backend. A good development process was used, which enabled for fast iterations with no cost in quality, and an excellent opportunity to learn and implement new things. Regular meetings were held—both technical and managerial—where everything was well discussed, planned, and coordinated, so everyone knew what they were doing and how it fits into the bigger picture.

  • Website for a Real Estate Company

    A responsive website built using a modern JavaScript framework with data being pulled from a headless CMS as well as an internal data store. The project was built from the ground up by a small team with the idea of using the newest available technologies while giving content managers a powerful tool that could seamlessly be integrated into the project's toolchain.

    We were able to completely separate data entry from the codebase which gave us more time to focus on the code itself. Continuous integration was set up from the very beginning, and everything was tested thoroughly with unit, integration, E2E (Cypress), and quality (Lighthouse) tests which allowed for quick and determined changes. Since the framework we were using leveraged server-side rendering (SSR), SEO was brought to a really high level, and could easily be controlled through the external CMS. The CMS also allowed us to easily set up a preview environment where content managers could see their edits live, enabling them to publish their changes only when they were satisfied with the result.


  • Languages

    HTML, CSS, Python, JavaScript, CSS3, HTML5, TypeScript, PHP
  • Frameworks

    Django, Next.js, Flask,
  • Libraries/APIs

    React, jQuery, SQLAlchemy, Backbone.js, jQuery Mobile, Node.js
  • Tools

    Git, GitHub, GitLab, VS Code, Sublime Text, ITerm, Figma, Slack, Notion
  • Paradigms

    Unit Testing, E2E Testing
  • Platforms

    Contentful, Linux, MacOS, Visual Studio Code, Google Chrome, Docker
  • Other

  • Storage

    PostgreSQL, MySQL, Redis


  • Master's Degree in Telecommunications and Informatics
    2008 - 2014
    University of Zagreb, Faculty of Electrical Engineering and Computing - Zagreb, Croatia

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