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François KoesslerFK

François Koessler

Senior Ruby on Rails & Typescript Developer

€600/day
11 projects
Strasbourg, FR
15+ years

Average response time: 1 hour

Freelancer profile translated to English.
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About François

+10 years of experience | Backend & Frontend Development | E-commerce & Startups | Ruby on Rails & Typescript | INSA Lyon Engineer

> Why trust me?

Senior web developer, I support startups and SMEs in the design, development, and optimization of their e-commerce platforms and web applications.

My profile covers backend (Ruby on Rails), frontend (Turbo, Stimulus, React, Next.js), and DevOps (deployment, CI/CD, monitoring), allowing me to manage projects from initial conception to the maintenance of mature applications, ensuring performance, scalability, and evolvability.

A graduate engineer from INSA Lyon, I combine technical rigor, product sense, and a pragmatic approach to deliver high-performing, scalable, and evolvable solutions aligned with business value.

> Key Expertise

E-commerce: custom e-commerce platforms, payment integration (Stripe, PayPal, ...), business automations, dashboards, and back-offices.

**Full-stack web development**: custom applications, API integration, performance, scalability, and maintainability.

**Architecture & DevOps**: CI/CD pipelines, server deployment (Ansible) or cloud (Google Cloud, AWS, Render, Heroku), monitoring, and optimization.

**Product & MVP Development**: rapid creation of robust and scalable products (Rails, Stimulus, REST/GraphQL APIs).

**Collaboration & Mentoring**: product team collaboration, code review, best practices, and knowledge transfer.

> They trusted me

I have collaborated with companies of various sizes such as startups Kelvin and Direct Market, jewelry stores Ordumonde, SMEs Visorando and Babasport, as well as the Carrefour group, on various web projects: SaaS tools, e-commerce platforms, and business applications.

đź“© Contact me now to discuss your project!
  • French

    Native or bilingual

  • English

    Fluent

  • Chinese

    Fluent

  • German

    Basic

Remote only
Primarily works remotely

Experience

  • kelvin technologies
    Development of a Whatsapp chatbot
    REAL ESTATE
    February 2024 - April 2024 (3 months)
    Paris, France
    Development of a custom Whatsapp chatbot integrated with the Kelvin web application backend.

    The chatbot's objective is to collect information about the user's home: various details, photos, and videos, then upload this information to the Kelvin web application back-office to initiate a new energy renovation project.
    Ruby on Rails whatsapp Stimulus GitHub
  • Babasport
    Consulting and Development
    ENTERTAINMENT AND LEISURE
    April 2020 - Today (6 years and 2 months)
    Paris, France
    Technical lead on the Babasport web application based on the Ruby on Rails framework, consulting and development.

    I am responsible for Babasport:
    - Version upgrades from Rails 4 to Rails 8
    - Design and development of new features
    - Bug fixing
    - Backend and frontend performance optimizations
    - Integration with the Cloudflare service
    Ruby on Rails React.js Ruby Heroku Cloudflare
  • OR DU MONDE
    Consulting and Development
    E-COMMERCE
    July 2019 - Today (6 years and 11 months)
    Paris, France
    Technical lead on the OR DU MONDE web application based on the open-source e-commerce framework Spree, consulting and development.

    I am responsible for OR DU MONDE:
    - Version upgrade from Spree 1.2 to Spree 4.4
    - Design and development of new features
    - Bug fixing
    - Design and development of a frontend decoupled from the backend with NextJS
    Ruby on Rails JavaScript Ansible Next.js API

Reviews

5.0

Out of 10 ratings

GuillaumeG

Guillaume

kelvin technologies

Reviewed on 2/7/2025

François is a freelance Ruby on Rails developer of exceptional skill, who played a crucial role in delivering high-quality features to our clients. Collaborating closely with our team of experts for several months, he integrated seamlessly. He demonstrated a remarkable ability to meet our team's quality requirements while maintaining the necessary speed of execution. He stands out for his expertise and his ability to propose tailor-made solutions, perfectly adapted to our needs. I recommend him warmly and with the utmost confidence.
A

Antoine

Babasport

Reviewed on 7/8/2020

Top-notch, deadlines met. Autonomy, responsibility. In short, to be recommended!

Recommendations

AP
Sacha PavanSP
AR
+5
Antoine Petit and 7 other people have recommended François

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Education

  • Engineer
    INSA Lyon
    2008

Skill set

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