Wael Almattar, Back-end Developer in Berlin, Germany
Wael Almattar

Back-end Developer in Berlin, Germany

Member since October 1, 2020
Wael is an ambitious freelance senior software engineer and agile evangelist with over eight years of experience in web development, performance optimization, and architecture design. Thanks to a proactive attitude, an open mind, and an entrepreneurial spirit, Wael's managed international and distributed teams to deliver products on time and within budget. In a nutshell, Wael lives and breathes software development.
Wael is now available for hire


  • Klarna
    Node.js, TypeScript, Amazon Web Services (AWS), Microservices, Apache Kafka...
  • Zalando
    Node.js, TypeScript, Amazon Web Services (AWS), NPM, Microservices, Storybook...
  • Anheuser-Busch
    Node.js, TypeScript, React, GRAPH, REST APIs, Apache Kafka, Microservices...



Berlin, Germany



Preferred Environment

Amazon Web Services (AWS), SQL, TypeScript, REST APIs, Microservices, Node.js, Go, Ethereum Smart Contracts, Solidity, Cosmos SDK

The most amazing...

...project I've done was designing and implementing a platform that serves more than 12,000 companies and 100,000 users.


  • Senior Back-end Engineer

    2021 - 2022
    • Worked in a team of eight people to develop and maintain browsers within the Klarna application.
    • Took responsibility for the back-end infrastructure of the back-end facing front-end layer and internal service to serve Klarna users.
    • Used Node.js and TypeScript to develop and maintain back-end services that handle more than 10 million daily requests.
    • Wrote testable, documented code that was highly maintainable.
    • Ensured maximum performance, compatibility, and a world-class user experience across devices and form factors.
    • Stayed up to date on emerging technologies and frameworks.
    Technologies: Node.js, TypeScript, Amazon Web Services (AWS), Microservices, Apache Kafka, Redis, Axios, Back-end Development, Solution Architecture
  • Senior JavaScript Engineer

    2020 - 2020
    • Used modern web technologies and frameworks to develop front-end distribution systems for components and libraries across the whole retail center.
    • Wrote testable, documented code that was highly maintainable.
    • Developed for maximum performance, compatibility, and a world-class user experience across all devices and form factors.
    • Collaborated with UI/UX designers to improve usability and accessibility.
    • Automated repetitive tasks when possible, using customized scripts.
    Technologies: Node.js, TypeScript, Amazon Web Services (AWS), NPM, Microservices, Storybook, Antd, GraphQL, Back-end Development
  • Lead Software Engineer and Architect

    2019 - 2020
    • Spearheaded the back-end infrastructure development for a new payment service in the Southern American region with an expected 1 million daily users.
    • Designed the overall back-end framework (security, documentation, deployment, testing, and so on).
    • Implemented an e-wallet, single-page application with React and Webhooks.
    • Created checkout components for external usage by customers and published them to the npm library.
    • Collaborated with a team of ten developers to implement back-end services by GraphQL.
    • Worked with the rest of the squad and external service providers to ensure the back-end services needed in each iteration were delivered.
    • Ensured that the pace of delivery was protected by applying best engineering practices.
    • Offered a strategic direction on best design practices.
    • Provided updates to date documentation at every stage of development.
    Technologies: Node.js, TypeScript, React, GRAPH, REST APIs, Apache Kafka, Microservices, Azure, Azure Cloud Services, Kubernetes, NoSQL, MongoDB, Payment APIs, Payment Processing, Fintech, PostgreSQL, Architecture, Back-end Development, Solution Architecture
  • Lead Back-end Developer (Node.js)

    2018 - 2019
    • Worked with engineering managers to construct the new team to build a new platform used by the Yara sales team in more than ten countries.
    • Constructed a project with TypeScript, GraphQL, and caching, using Redis on the back end and React with hooks and Material-UI on the front end.
    • Consulted the business team to draw a reliable roadmap.
    • Worked mainly as a back-end developer during my time here.
    • Interviewed candidates for permanents roles to continue working on the project.
    • Worked with the SRE team to ship deployments with CircleCI, Docker, and Kubernetes.
    Technologies: Amazon Web Services (AWS), Unit Testing, Auth0, SQL, Kubernetes, Docker, MUI (Material UI), Elastic, Redis, GraphQL, TypeScript, Node.js, Back-end Development
  • Lead Back-end and Microservices Engineer

    2017 - 2019
    • Developed the back end for a platform that serves 100,000 users and 12,000 companies.
    • Took responsibility as a lead programmer for the whole back-end infrastructure, including microservices and RESTful APIs.
    • Proposed a simplified but scalable system architecture that is being used at the moment in the production environment.
    • Introduced GraphQL to the platform and worked with the front-end team to integrate it.
    • Used automated solutions to accelerate the development process.
    • Extended the existing API with more features and functionalities.
    • Tracked tasks, features, and bugs with Jira and Asana.
    • Implemented a data-driven approach to support the marketing and sales teams.
    • Created a one-page application using React and custom components on top of MUI v4.
    • Worked with the business development manager on breaking down new business models into realistic technical tasks with a clear roadmap.
    Technologies: Auth0, SQL, PostgreSQL, REST APIs, RESTful Development, APIs, Cron, Git, Koa, AMQP, RabbitMQ, React, GraphQL, Microservices, Node.js
  • React Developer

    2017 - 2017
    International Committee of the Red Cross (via Iosbar Blue Infinity)
    • Developed a custom CRM system for the International Committee Red Cross.
    • Tracked features and fixed bugs using Microsofts TFS platform and Microsoft PBI. The platform has been launched successfully and has been in production used internally by ICRC.
    • Provided full unit testing and clear documentation.
    Technologies: Git, Amazon Web Services (AWS), Jest, TypeScript, Node.js, React
  • Full-stack Developer

    2017 - 2017
    • Implemented a single-page, live-map platform to show users and shops.
    • Extended the API for the Dether.io platform with a couple of endpoints.
    • Formulated and documented technical architecture, components, and strategies for mitigating technical challenges.
    Technologies: Git, React Native, Google Maps, Mapbox, Redux Form, Jest, Redux, React, Node.js
  • Full-stack Developer

    2016 - 2017
    • Worked part-time with the core team to grow the main back-end server using Node.js.
    • Implemented new features and pages using React for A/B testing software.
    • Wrote unit, end-to-end, and integration tests using Mocha and Jest.
    • Optimized the performance by moving aggregated data to Redis server storage.
    • Implemented an A/B testing solution to determine the better-performing variations.
    Technologies: Mocha, Git, Heroku, Redux, Testing, Jest, Express.js, Redis, Node.js, React
  • Software Engineer

    2015 - 2016
    Globe IT
    • Designed a complete tracking system for GPS tracking devices with a live real-time dashboard using Node.js, Socket.IO, and AngularJS.
    • Created and designed a decoder server to handle a GPS binary device’s data and send commands.
    • Optimized a web application's speed and data structures by combining Memcached and MySQL databases.
    • Led the API development of a new eCommerce/digital platform (PHP and Node.js).
    • Designed a dashboard along with a complete solution for a chat module for an eCommerce project using PHP and AngularJS.
    • Maintained existing eCommerce and digital applications to meet the ever-evolving demands of the business (PHP).
    • Implemented an online payment system for eCommerce services.
    • Developed from scratch an interactive web conference video platform that hosted video rooms with text and voice capabilities using WebRTC, Socket.IO, and jQuery.
    • Used AngularJS as the development framework to build a dashboard, a single-page application, and a more interactive front end.
    • Developed a web-scraping application along with the entire server-side application using Python.
    Technologies: SQL, Git, C++, Loopback, WebRTC, Python, MySQL, Zend Framework, jQuery, CSS, PHP, Redis, Express.js, Socket.IO, AngularJS, Node.js, Back-end
  • Web Developer Intern

    2014 - 2014
    • Worked on various projects where more experienced, senior developers guided me.
    • Integrated and tested an online payment system to the eCommerce platform.
    • Worked primarily as a full-stack developer as part of my bachelor's degree thesis.
    Technologies: CSS, SQL, JavaScript, PHP, Zend Framework


  • Back-end Infrastructure for Two APIs and Six Microservices

    As the lead back-end developer, I was responsible for rewriting one API and extending the features on the other one along with six microservices connected to third-party solutions. I introduced scalable, modern technologies implemented and used nowadays in production to serve more than 100,000 daily users.

  • Lead Back-end Consultation

    I proposed and led the development of a back-end infrastructure of a nutrition plan generation platform used by the sales team at an $8-billion valued fertilizer producing company (a company that was established in 1905). The back end was integrated with an already existing agronomical engine and SSO authentication service.

  • GEO2 | Live Tracking System for Cars, People, or Animals

    For this project, I first built a back-end server that decodes binary signals from geolocation devices. Then I implemented a single-page application to show real-time data on maps. The application was designed both for web and mobile devices. The platform supports multiple users per partner and also has an online payment system.

    The devices and platform are used by more than 20 partner companies.


  • Languages

    GraphQL, TypeScript, JavaScript, HTML, C++, SQL, C, Python, PHP, CSS, Go, Solidity
  • Frameworks

    Koa, AngularJS, Express.js, Zend Framework, Loopback, Jest, Redux, React Native, MUI (Material UI), Angular, Tendermint
  • Libraries/APIs

    Node.js, React, Socket.IO, React Redux, jQuery, WebRTC, Redux Form, Google Maps, AMQP, Objection.js, Segment.io, REST APIs, Antd
  • Paradigms

    Microservices, Microservices Architecture, RESTful Development, Unit Testing, Automation, Management, Testing
  • Other

    APIs, Back-end, Back-end Development, Computer Science, Algorithms, Web Programming, Software Engineering, Data Structures, RESTful Microservices, HubSpot, Code Auditing, Cryptography, Machine Learning, Data Analytics, Mobile App Development, Space Dynamics, Communication, Custom Instruments, Space Physics, Artificial Intelligence (AI), Space Electronics, Astrophysics, Image Processing, Microcomputer Engineering, Dynamics and Control, Intercom, Full-stack, GRAPH, Payment APIs, Payment Processing, Fintech, Storybook, Axios, Cosmos SDK, Architecture, Solution Architecture, Ethereum Smart Contracts
  • Tools

    Git, RabbitMQ, Cron, CircleCI, Slack, Elastic, Mocha, GIS, Auth0, NPM
  • Platforms

    Amazon Web Services (AWS), Algolia, Heroku, Mapbox, Docker, Kubernetes, Apache Kafka, Azure, Blockchain
  • Storage

    Redis, MySQL, PostgreSQL, Azure Cloud Services, NoSQL, MongoDB


  • Joint Master's Degree in Space Science and Technology
    2016 - 2017
    Université Paul Sabatier Toulouse III - Toulouse, France
  • Completed Credits Towards a Joint Master's Degree in Space Science and Technology
    2016 - 2016
    Luleå University of Technology - Kiruna, Sweden
  • Completed Credits Towards a Joint Master's Degree in Space Science and Technology
    2015 - 2016
    The Julius Maximilians University of Würzburg - Würzburg, Germany
  • Bachelor's Degree in Computer Science
    2012 - 2015
    Warsaw University of Technology - Warsaw, Poland


  • Fifth Place in a Collegiate Programming Contest
  • Bronze Medal
    International Olympiad in Informatics (IOI)

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