Joseph Halter, Developer in Hobscheid, Luxembourg
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Joseph Halter

Verified Expert  in Engineering

Software Developer

Hobscheid, Luxembourg
Toptal Member Since
February 10, 2015

After having worked as a developer in finance for several years, Joseph transitioned to a contracting role, which allowed him to gain experience across diverse industries, including HR, entertainment, and healthcare. He has collaborated with organizations of all sizes, ranging from startups to Fortune 500 companies.


Openhood sarl
RabbitMQ, PostgreSQL, Ember.js, Elixir
Talentbox SA/Metrilio SA
PostgreSQL, Ruby on Rails (RoR), JavaScript, CSS, HTML
Kneip Communication SA
MongoDB, PostgreSQL, Ruby on Rails (RoR), JavaScript, CSS, HTML




Preferred Environment

Visual Studio Code (VS Code), Git

The most amazing...

...accomplishment I've had was participating in a Pfizer project that expedited the delivery of crucial medicines, including the COVID-19 vaccine.

Work Experience


2016 - PRESENT
Openhood sarl
  • Consulted for various small to medium businesses.
  • Scaled a transactional REST API to multiple servers using RabbitMQ for messaging between the servers.
  • Created a static website generator tailored to the specific needs of a customer.
  • Used Ember.js and Semantic UI to create a single-page web application for both mobile and desktop users.
  • Created a marketplace with exchanges in multiple currencies and real-time chat between the users.
  • Created a multiplayer 3D web game using Babylon.js and Elixir/Phoenix with GraphQL for the back end.
  • Created a single-page application React website with animated components, front-end side tests, and a library of components using Storybook with responsive design for mobile/tablet/desktop. Used GraphQL with Elixir/Phoenix in the back end.
  • Handled GDPR compliance for a very large Rails application including integration with 10+ external providers, each with their own API integration, including Stripe, Onfido, Braze, AppsFlyer, Mailchimp, ZenDesk, and more.
  • Organized a web-based contest where people can win a $100,000 free roll then later a $250,000 free roll with timer, real-time charts and visualizations, email notifications, a full web admin interface with filtering and reporting with exports in multiple formats.
  • Allowed people to sign up using Twitter, Facebook, or email, track the signed-in user's Twitter friends, and allowed the user to share multiple events with their followers, optimize display of posts on Twitter as a nice card, and optimize for a perfect Google page speed score.
Technologies: RabbitMQ, PostgreSQL, Ember.js, Elixir

Senior Developer

2011 - 2016
Talentbox SA/Metrilio SA
  • Migrated a dozen separate customer-specific Rails applications into a new unified configurable online platform, reducing the time to set up a new customer from one month to three days.
  • Maintained a very large Rails codebase with hundreds of tables and models, undergoing several re-factoring processes to always allow for adding new features while keeping maintenance time under control.
  • Added thousands of integration tests to avoid regressions, reduce errors, and reduce the need for human testing, which was previously a full-time job for one person.
  • Improved production from one deployment per month to multiple deployments per day.
Technologies: PostgreSQL, Ruby on Rails (RoR), JavaScript, CSS, HTML

Software Architect

2009 - 2011
Kneip Communication SA
  • Created a platform for financial institutions to browse their fund publication matrix, allowing them to view and search in real time inside the content of a report that the company couldn't generate daily anymore due to a stressed Oracle database with a lot of stored procedures.
  • Built a multiple-internal API to synchronize legacy applications developed in different programming languages together.
  • Programmed a mail robot API to communicate with ClearStream during all the steps of the fund creation in order to get a new ISIN code.
  • Developed a new platform to centralize all the documents related to funds and allow fast batch import of data in a bi-temporal database with a very complex permission system.
Technologies: MongoDB, PostgreSQL, Ruby on Rails (RoR), JavaScript, CSS, HTML

Computer Programmer

2006 - 2009
Akira Web SA
  • Created a website in 17 languages for Chanel promoting their latest perfume.
  • Built a communication platform for the leadership of a leading international steel and mining company via SMS notifications.
  • Programmed an in-house CMS in PHP to power websites localized in many languages, allowing people to create their own forms and wizards and bind them to multiple custom services.
  • Handled multiple dedicated servers and scaled PostgreSQL to multiple servers.
  • Started using Rails more and more often to develop prototypes even faster.
Technologies: Ruby on Rails (RoR), PostgreSQL, Flash, MySQL, PHP, JavaScript, CSS, HTML


2006 - 2006
Artic Media Sàrl
  • Created a platform to find real estate based on geolocation grouped by labor pool.
  • Built a website for a jewelry store with great attention to usability and accessibility.
  • Programmed a website for a big local shopping center from scratch and worked on SEO until it was in the top 10 on Google searches for all relevant keywords, and even ranked 1st when searching on just the name of the city for multiple months.
  • Organized online contests where it's possible to win real money, and worked on preventing people from being able to cheat the system.
Technologies: Flash, MySQL, PHP, JavaScript, CSS, HTML


2005 - 2006
Lorweb Sàrl
  • Converted manual entries for a local football team into a searchable database with intelligible charts.
  • Extended an in-house CMS to allow customers to create new pages in multiple languages more easily.
  • Created a task to load, parse, and sync multiple directories of XML files with an online database.
  • Scaled a Microsoft SQL-based website by creating specific indexes and optimizing query speed for paginated objects.
Technologies: Microsoft SQL Server, ASP.NET, JavaScript, CSS, HTML


2001 - 2005
Ekzakt Sàrl
  • Managed customer expectations; responsible for estimates and team planning.
  • Launched a successful multilingual online store to sell art pieces.
  • Converted 2D schematics into 3D graphics, improved customer/dealership communication, and learned how to register a patent.
  • Helped a customer digitize his growing paper documents archive.
  • Taught clients webmaster skills necessary to keep their company websites up-to-date.
  • Used Flash vector and scripting capabilities to create responsive websites, serving different content depending on resolution.
Technologies: Blender, Flash, MySQL, PHP, JavaScript, CSS, HTML

Metrilio HR Software

An HRIS solution used daily by thousands of employees across the world.

Kneip Master File for Fund Data Management
A Rails project to manage your financial fund by ISIN code using a bi-temporal database.

KNEIP Publication Matrix
To have an overview of where each of your fund legal publications are published across the world.

A Sequel plugin for bi-temporal data.
1998 - 2000

DEUG (Equivalent to Bachelor's) Degree in Computer Science

Université de Metz - France


REST APIs, Ember Data, jQuery, PayPal API, Sequel, React, Ruby on Rails API, React Redux, JSON API, SendGrid API, Immutable.js, Babylon.js, Node.js, Three.js, Vue


React Apollo, GitHub, Cucumber, RSpec, Git, GitLab, JSS, SendGrid, Vim Text Editor, AWS SDK, JavaScript Debugging, Flash, Blender, RabbitMQ, Webpack, Webpack 4, Webpack 3, Webpack 2


Phoenix, Ember.js, Sinatra, Ruby on Rails (RoR), Jest, Redux, Ruby on Rails 3, Ruby on Rails 4, Ruby on Rails 5, Bootstrap, Business Rules Engine, Bootstrap 3, Bootstrap 2, Bootstrap 3+, ASP.NET, Unity3D, RubyMotion, Express.js


SCSS, Elixir, JavaScript, Ruby, CoffeeScript, CSS, HTML, TypeScript, GraphQL, CSS2, CSS3, SQL, HTML5, HTML4, ECMAScript (ES6), JavaScript 5, JavaScript 6, TypeScript 2, TypeScript 3, PHP


Testing, Test-driven Development (TDD), Behavior-driven Development (BDD), Functional Programming, Refactoring, Pair Programming, REST, Object-oriented Programming (OOP), Agile Software Development, Continuous Integration (CI), Requirements Analysis, Continuous Deployment, Web Architecture


Godot, Heroku, Mailgun, Amazon Web Services (AWS), Visual Studio Code (VS Code)


PostgreSQL, PostgreSQL 10, JSON, MySQL, Amazon S3 (AWS S3), Memcached, Redis, Microsoft SQL Server, MongoDB


Single-page Applications (SPA), Responsive UI, API Integration, Ember CLI, Prototyping, Regular Expressions, Application Security, APIs, Workflow Modeling, Software Architecture, Bitemporality, Pub/Sub, Web Components, Scalability, User Experience (UX), Debugging, Architecture, Visualization, Ruby Gems, Ruby Performance, JavaScript Libraries, CSS Grid, CSS3 Animation, User Interface (UI), eCommerce, Technical Leadership, Apollo, App UI, App UX

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