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Sébastien KempfSK

Sébastien Kempf

Web Developer | React.js | Next.js | Typescript

€500/day
4 projects
Paris, FR
3-7 years

Average response time: 1 hour

Freelancer profile translated to English.
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About Sébastien

Web Developer | React.js | Next.js | TypeScript

Your web application is showing its limits? Your no-code MVP is no longer enough?

You launched anMVPwithno-codeorlow-codetools, but today you are facingperformance**, **stability**, or **scalabilityissues? Your application can no longer absorbgrowthandnew featuresare becoming complicated to implement?

I can help youtake over your existing codebaseor develop a new product with a modern stack: **React.js, Next.js**, and **TypeScript**. My role is to transform your application into a reliable, maintainable tool designed for growth.

Web developerwith over 5 years of experience, I have supported startups, solopreneurs, SMEs, and large corporations such asDeezer**, **Piaget**, and **Roger Dubuison:
  • Creation of MVPs and SaaS applications
  • Redesign of existing applications
  • Business dashboards and reporting tools
  • Landing pages optimized for conversion
My all-inclusive approach:
  • Clean code and clear architecture inReact.jsandNext.js
  • Strong typing withTypeScriptto reduce bugs
  • Reusable components and modern best practices
  • Stable, performant, and scalable deliverables
Technical stack: React.js, Next.js, TypeScript, JavaScript, TailwindCSS, Shadcn, REST & GraphQL APIs, Prisma, Stripe, Vercel ...

Why work with me?
  • Transparent communication throughout the project
  • Business-oriented product vision
  • No technical debt, scalable code from the start

Looking to launch your web project or redesign your application?
Contact me to schedule a video call and let's build a clear roadmap together from idea to deployment.

#Readytohelp
  • French

    Native or bilingual

  • English

    Native or bilingual

Can work on-site
Paris (up to 50km), Lyon (up to 50km), Marseille (up to 50km), Bordeaux (up to 50km), Toulouse (up to 50km)

Experience

  • Eloïse Entertainment
    Malt logoOn Malt
    Development of an automated planning tool
    CULTURE
    October 2025 - October 2025
    Paris, France
    → Mission Objective:
    Develop a centralized platform to automate music event coordination, eliminating error risks and reducing administrative burden.

    → Achievements:
    • Development of an intuitive interface in React.js / Next.js with a role-based custom view system (organizer, artist, technician), ensuring immediate adoption without training.
    • Architecture of automated notifications with scheduled SMS/email sending (Twilio, Resend), real-time conflict detection, reducing manual follow-ups by 70%.
    • Implementation of a dynamic timeline system with an optimized mobile view for the D-day, enabling efficient field management and increased responsiveness to unforeseen events.

    → Technical Stack:
    React.js, Next.js, TypeScript, PostgreSQL, Prisma ORM, Twilio, Resend, TailwindCSS, Vercel
    Web Development Front-End Development React.js Next.js Typescript
  • VinoMemo
    Web Developer | React.js | Next.js | TypeScript
    WINE AND SPIRITS
    August 2025 - September 2025 (1 month)
    Paris, France
    → Mission Objective:
    Develop a professional wine tasting note-taking application (web and mobile), combining **SEO**, **accessibility**, and **performance**.

    → Achievements:
    • Development of a modern application inReact.js/Next.jswith a customShadcntheme, ensuring a high-end user experience and enhanced perceived quality.
    • Implementation of a serverless architecture with Supabase (auth, Google and Apple OAuth, DB) and Drizzle, guaranteeing scalability, speed, and time savings in development and maintenance.
    • Integration of web & product analytics + error tracking (PostHog) for increased product visibility, data-driven decision-making, and continuous performance improvement.

    → Technical Stack: React.js, Next.js, React Native, Expo, TypeScript, Supabase, Drizzle, PostHog, Playwright, Shadcn UI
    Web Development Front-End Development React.js Next.js Typescript
  • Deezer
    Web Developer | React.js | Next.js | TypeScript
    ENTERTAINMENT AND LEISURE
    January 2022 - June 2025 (3 years and 5 months)
    Paris, France
    → Mission Objective:
    Develop and maintainweband Smart TVapplications(Music Quizz, Deezer Partners, Web SDK, Partner Portal) while designing SDKs and APIs for partners, to ensure **performance**, **scalability**, and a **high-end user experience**.

    → Achievements:
    • Creation ofmodern front-end interfaceswithNext.js**, **React.js**, **TypeScript**, and **TailwindCSS**: **responsiveintegration,reusable components**, **new features**, and **performance optimizationfor increased visibility and perceived quality.
    • Maintenance and evolution of Smart TV apps (Music Quizz Party Mode, OAuth, rebranding, tracking, bug fixes, release management), generating+1k new weekly usersand strengthening reliability and engagement.
    • Design of partner tools and integrations (Deezer Partners, Web SDK, back office, QA tooling): proof-of-concepts, Cypress end-to-end tests, robust APIs, facilitating+505k subscriptionsvia RTL and15k daily additionsof tracks from TikTok, with significant time savings for the teams.

    → Technical Stack:
    Next.js, React.js, TypeScript, JavaScript, Redux, TailwindCSS, Radix UI, Shadcn, Chakra UI, Cypress, Jest, Auth0, Node.js, Docker, Kubernetes, Jenkins
    Web Development Front-End Development React.js Next.js Typescript

Reviews

5.0

Out of 4 ratings

EloïseE

Eloïse

Eloïse Entertainment

Reviewed on 10/20/2025

Sébastien delivered our event management MVP in 5 days as promised. Impeccable daily communication, clear process from the start. The tool automates our schedules, reminders, and detects time conflicts. Exactly what we needed for our March festival. We're already saving 10 hours/week on coordination. What amazed me: he understands the business, not just the tech. Zero jargon, all concrete. The best tech investment we've made. Go for it!
AD

Account deleted

Reviewed on 2/8/2021

Great, Sébastien is a very good developer who knows how to advise and support his client in the best way until the end of the mission. I recommend Sébastien for your mobile application development projects.

Recommendations

Mathieu SiaudeauMS
MN
FU
+1
Mathieu Siaudeau and 3 other people have recommended Sébastien

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Education

  • Application Designer Developer
    Le Réacteur
    2020
    Développement d'interface Front End (React.js, Next.js, Typescript, Javascript, ChakraUI), développement Back End (Node.js, Typescript, Express, MongoDB), développement Mobile (React Native, Expo)
  • Full stack JavaScript Web and Mobile
    Le Reacteur
    2020
    Développement d'interface Front End (HTML5, CSS3, Javascript, React.js), Développement Back End (Node.js, Express, MongoDB), Développement Mobile (React Native, Expo)

Certifications

  • Professional title level 6: Application Designer Developer (RNCP)
    Ministry of Labour
    2023
  • Professional Scrum Master I
    Scrum.org
    2021

Skill set

Categories