Emmanuel Cousin
Senior Software Engineer - Ruby on Rails - Javascript
Professional Status
Freelancer
Available
About Me
Hi! I'm Emmanuel, a senior software engineer with 10 years of experience in Ruby on Rails and JavaScript.
I've helped startups scale their systems and teams during growth phases, balancing fast delivery with quality code. I bring deep technical knowledge that raises the bar for the whole team and work well with people across the company.
I mentor junior developers and build solutions for sustainable growth.
Currently available and looking for my next opportunity. Looking forward to connecting!
I've helped startups scale their systems and teams during growth phases, balancing fast delivery with quality code. I bring deep technical knowledge that raises the bar for the whole team and work well with people across the company.
I mentor junior developers and build solutions for sustainable growth.
Currently available and looking for my next opportunity. Looking forward to connecting!
Senior Software Engineer
Gumroad
Since August 2025
- Authored 68 merged PRs (48K+ lines, 889 files) and reviewed 425+ PRs in 6 months as a Senior Full-stack engineer on Gumroad, a digital product e-commerce platform serving hundreds of thousands of creators and millions of buyers worldwide, processing payments through Stripe and PayPal.
- Led the company-wide frontend architecture migration from ERB/React on Rails to Inertia.js/React — designed the multi-phase modernization roadmap (Inertia adoption, legacy dependency removal, Webpack-to-Vite transition), authored architectural guidelines and coding standards, and decomposed the initiative into 42+ individually-scoped tasks enabling parallel execution by internal and open-source contributors. Drove 25+ page migrations to completion in 3 weeks through hands-on code review and mentorship.
- Transitioned Gumroad's entire admin panel from ERB to Inertia.js/React — established the Inertia.js architecture, migrated 6+ admin pages with presenter patterns and infinite scroll, then removed ~4,000 lines of legacy code.
- Shipped major payments and billing features, including a full implementation of the subscription restart lifecycle on Stripe and automated fraud detection improvements. Extracted reusable domain concerns (AttributeBlockable, ChargeProcessable) from complex business logic to improve codebase maintainability.
- Orchestrated delivery of 270,000+ personalized Year in Review emails, each requiring multiple Elasticsearch aggregation queries (creator ranking, sales analytics, geographic breakdowns). Built idempotent production scripts resilient to remote console disconnections to manage the multi-day send operation.
- Delivered the Black Friday 2025 promotional feature for Gumroad's Discover marketplace. Maintained platform health through proactive Rails upgrades, security vulnerability fixes, CI/CD pipeline health ownership, and automated developer tooling.
Senior Software Engineer
Spring
June 2024
to April 2025
Oslo
Norway
- I helped the company transition from a DeFi platform to a full CeFi marketplace, which involved major code refactors, delivering new features, and raising the engineering team's overall technical standards.
Senior Software Engineer
Rendez-Vous Digital
July 2021
to April 2024
Cannes
France
- At Reprtoir, a software-as-a-service platform driving innovation in the music industry, I collaborated with a team of skilled Ruby on Rails experts. Together, we contributed to significant business initiatives for the company.
Lead Developer
Small Door Veterinary
January 2021
to July 2021
New York
United States - New York
- As part of my role overseeing the maintenance and feature development of web and mobile apps, I facilitated the shift in the company's product development strategy. We transitioned from relying on external consultants for a single veterinary practice to establishing an internal team of diverse specialists, serving multiple practices across various regions.
Senior Developer
Braidio
February 2019
to January 2021
Los Angeles
United States - California
- During my tenure at Braidio, I worked as a contractor, collaborating with a distributed team of exceptionally skilled developers. Our primary focus encompassed the integration of third-party apps, development of innovative features, reinforcement of data protection measures, and overall improvement of the code base.
Software Engineering Consultant
ECN Ventures
Since January 2018
Freelancer
- General software development
- App creation from scratch
- Quality, security and performance audits
- APIs conception & integration
- Web services integration
- Infrastructure management
- Mobile development
- Coaching for junior developers
Fullstack Web Developer
My Job Glasses
July 2017
to December 2017
Full-time
Paris
France
- Successfully initiated the launch of V2, covering both back and front ends.
- Introduced a KANBAN workflow within the technical team.
- Implemented efficient inter-team processes across the company.
Web developer Ruby on Rails
Captain Contrat
January 2015
to July 2017
Full-time
Paris
France
- Implemented numerous features improving the main app
- Implemented an automated invoicing service fully integrated to the main business workflow
- Created a customer service dashboard for the Customer Success Team
- Created a survey editor which hosts all of Captain Contrat's questionnaires, as well as a generic iframe-based displaying module
- Development of the startup's inner culture and values
- Improvement of the Dev team's current workflow
- Ran training worshops about internal tool best practices and technical skills
Product Manager - Amadeus
Alten
December 2012
to October 2014
Full-time
Sophia-Antipolis
France
- Global scale Project Management
- Product Management: business needs, requirements, functional specs, budget, benchmarking, etc.
- Business models, marketing studies
- Intrapreneurship
-
Ruby on Rails, HTML, CSS
Expert
-
MySQL, Postgres, MongoDB
Expert
-
Javascript, React.js, Hotwire
Expert
-
Mobile develop
Expert
-
Automated Testing (Minitest, Rspec)
Expert
-
Git, GitHub, Gitlab
Expert
-
Docker, AWS, Heroku, Scalingo
Advanced
-
Redis, ElasticSearch, Algolia
Advanced
-
Shape Up advocate
Expert
-
Lean development with KANBAN
Advanced
-
Agile development with SCRUM
Expert
-
React Native
Advanced
-
Hotwire Native
Advanced
-
Progressive Web Apps (PWAs)
Expert
-
English
Expert
-
French
Expert
-
Portuguese
Good
-
German
Intermediate
Certificate of Applied Sciences:
- Engineering project management
- Budget management
- Functional analysis and methods
- Quality management
- Change management
https://www.usherbrooke.ca/
Graduated as an Engineer from École Centrale de Lille, specialisation in Industrial and Entrepreneurial Engineering.
https://iteem.centralelille.fr/
https://iteem.centralelille.fr/
