Hadrien Pierart, Developer in Nantes, France
Hadrien is available for hire
Hire Hadrien

Hadrien Pierart

Verified Expert  in Engineering

Web Developer

Nantes, France
Toptal Member Since
November 7, 2018

Since 2012, Hadrien has been building websites and apps using a range of web and mobile frameworks and techniques and this work has helped him to obtain a strong understanding of an app's UX/UI. He also has worked as an InfoQ editor and a JavaScript/HTML5 trainer, building up his sharing skills and pedagogy. Conciseness, professionalism, and the ability to explain complicated technical points help him communicate with anyone.


Training & Training Content Development, Training, TypeScript, Git...
Confidential Client
Git, JavaScript 6, Responsive UI, Front-end, CSS, JavaScript, HTML5, React
Cotation Santé
Git, JavaScript 6, Responsive UI, CSS, JavaScript, React Native




Preferred Environment

React Native, React, Git, IntelliJ IDEA, Linux

The most amazing...

...thing I've built was a React Native app from scratch (with no prior experience) and its design. It's now used by hundred of general practitioners.

Work Experience

Senior Front-end Developer

2019 - 2020
  • Built a new application from scratch for a new BU.
  • Trained junior developers in React and front-end technologies.
  • Established the testing tools (unit, E2E, UI).
Technologies: Training, Training & Training Content Development, TypeScript, Git, JavaScript 6, Responsive UI, Front-end, CSS, JavaScript, HTML5, Cypress, Enzyme, Jest, GraphQL, React

Web Lead | Web Developer

2017 - 2018
Confidential Client
  • Implemented specific server-side rendering to build a metadata API on top of the web front (generating clean Facebook, Twitter, JSON-LD, and more).
  • Built a small scanning system to fetch elements in the database directly from their barcode.
  • Improved the performance of various web pages to 100 in Lighthouse.
  • Adapted the main website into a fully responsive version, with top-notch performances on mobile/3G networks.
  • Created fully static generated widgets for easy embedding, on top of the existing web app along with custom server side rendering.
Technologies: Git, JavaScript 6, Responsive UI, Front-end, CSS, JavaScript, HTML5, React

Web/Mobile Developer

2017 - 2018
Cotation Santé
  • Designed and structured an app, from the ground up and based on the users' feedback, to best fit the frequency of usage.
  • Built it, with React Native and Firebase, as an offline first experience and a cross-platform obligation.
  • Created a React website to go hand in hand with the app, with quick first and easy loading if displayed in the mobile app.
  • Compiled hundreds of cryptic rules from the administration into a simple interface and algorithm, easy to use for non-technical users.
  • Facilitated the daily routine of thousands of doctors in France with easier/quicker administrative tasks.
Technologies: Git, JavaScript 6, Responsive UI, CSS, JavaScript, React Native

Lead Web Developer

2015 - 2017
Once Dating
  • Developed the main website and application as a smooth responsive UI.
  • Built multiple back-office web apps with many D3.js graphs to browse the company's data.
  • Integrated small PR and marketing pages/sites.
  • Trained/mentored a younger web developer into becoming a great front-end developer.
  • Adapted the development of web tools and graphs to help mobile developers in their daily jobs, saving hundreds of hours of tedious/repetitive tasks.
Technologies: Training & Training Content Development, Training, Stripe API, Redux, Git, JavaScript 6, Responsive UI, Front-end, CSS, HTML5, React, AngularJS

Web Developer

2016 - 2016
  • Built a website with server-side rendering enabled for optimized SEO and performance.
  • Optimized the CSS and display for mobile (responsive) and PWA website.
  • Implemented a service worker for optimized loads and caching of resources/pages.
  • Optimized the performance and UI for a top ranking in Lighthouse.
  • Migrated an old PHP front-end into a beautiful React-based UI.
Technologies: Redux, Responsive UI, Front-end, HTML5, Webpack, SCSS, React

Web Developer

2014 - 2015
Axa Technologies
  • Developed a web intranet to create/start VM instances as a cloud provider.
  • Integrated multiple graphs through D3.js to monitor instances state.
  • Built a smart tutorial to help users pick the proper cloud provider.
Technologies: Front-end, HTML5, SCSS, Ember.js

Web Developer

2012 - 2014
Voyages SNCF Innovation
  • Integrated a map of France and Europe to display best offers for train travel.
  • Built rich markers and popups on top of the map.
  • Developed a rich system of navigation and bookmarking of searches to allow sharing of travels.
Technologies: Redux, Front-end, CSS, JavaScript, OpenStreetMap, Less, HTML5, jQuery, Ember.js

Cotation Santé App

Cotation Santé is a React Native/Firebase application and website to help doctors deal with the complexity of the health system declarations and administrative tasks in France. The app is built with the obligation of being fully available offline, but to reconnect and save data seamlessly on its own when a network is available

It is already used by more than 4,000 general physicians in France.

Once Dating

Once brings back magic to the online dating world. We launched at the end of 2015, with a slow dating approach that focuses on quality over quantity.

It is based on a seamless experience that works across all devices (Android, iOS, web) where you can browse for a date on your phone, then chat on your PC, and back on your phone in the evening.

The main website and landing page are built with performance in mind and designed with a sleek experience to help the users get comfortable quickly.


Hozana is the first French online social network dedicated to Catholic prayer. The platform aims at helping people band together to pray or exchange about various topics through small communities.

The main website was migrated from an old PHP app to a beautiful React application with an optimized performance.

Staff Santé

A small website with a revisited and more modern design to search for health-related jobs.

Staff Social

A small website with a revisited and more modern design to search for healthcare/social-related jobs.


I created a dedicated app for a new service based on React and Apollo/GraphQL.


JavaScript, HTML5, CSS, HTML, JavaScript 6, CSS3, SCSS, TypeScript, GraphQL, Less


React Native, Bootstrap, Jest, Redux, Cypress, AngularJS, Ember.js, Foundation CSS, Angular


React, Stripe API, jQuery


Responsive, Jobs to be Done (JTBD), BEM


Enzyme, Training & Training Content Development, Responsive UI, Training, Front-end, Mobile First, PWA, Progressive Web Applications (PWA), Happo, Apollo, OpenStreetMap, Fetch API, Personas, Ergonomic Design, Lean Startups, MVP Design, Startups


React Apollo, IntelliJ IDEA, Git, Mongoose, Figma, Webpack


Linux, Firebase, Google Cloud Platform (GCP), Webflow, Linux Mint


Neo4j, NoSQL, MongoDB

2010 - 2011

Master's Degree in Computer Science

Université Paris Dauphine - Paris, France

2007 - 2011

Master's Degree in Engineering

Agro ParisTech - Paris, France

Collaboration That Works

How to Work with Toptal

Toptal matches you directly with global industry experts from our network in hours—not weeks or months.


Share your needs

Discuss your requirements and refine your scope in a call with a Toptal domain expert.

Choose your talent

Get a short list of expertly matched talent within 24 hours to review, interview, and choose from.

Start your risk-free talent trial

Work with your chosen talent on a trial basis for up to two weeks. Pay only if you decide to hire them.

Top talent is in high demand.

Start hiring