Freelance React and Next.js development for SaaS and business applications
I build React applications for SaaS and business products, fully remote. At Leadbay (Y Combinator F25), I built the complete frontend from scratch, for the web app and its hybrid mobile app.
React projects I built
From a Y Combinator startup to a public institution, with my role on each project.
B2B prospecting platform, web and mobile
Sales teams discover leads on the web and on mobile; I designed the Redux architecture of the whole app and tested it end to end with Cypress
Personalised workout generator
One React 19 and Vite app runs in the browser, on iOS and Android through Capacitor and on Windows, in nine languages
Sciences Po · Confidential project
Academic portal, frontend and backend
A multi-zone Next.js 16 and React 19 frontend on a Spring Boot backend, with CAS sign-in, designed and built with another developer
Dashboard for AI corpus analysis
A test-driven React dashboard for managing the questions and answers its AI produces, with PDFs generated in React PDF
National website and dealer-site platform
A React back office over a REST API for the national website's content and business operations, with full frontend autonomy
Real-time wildlife monitoring on wind farms
Operators follow wildlife protection on their wind farms live, in a new React interface with Nivo charts, Leaflet maps and Azure AD sign-in
From user interfaces to application architecture
I develop SaaS frontends, business dashboards and reusable components, tested in continuous integration.
Around React, I adapt to the choices your codebase has already made: single-page apps with Vite or server rendering with Next.js, Redux or TanStack Query, and libraries such as shadcn/ui, Radix UI or Material UI.
Possible deliverables
- Frontend architecture, navigation and state management
- Reusable components documented in Storybook
- Cypress and Vitest tests in continuous integration
- Assessment, takeover and maintenance of an existing React application
- Node.js or Java backend work for a full-stack engagement
- Engagement
- Team support, project or application takeover
- Schedule
- Agreed for the engagement
- Indicative rate
- €550 excl. VAT / day (October 2026)
- Collaboration
- Fully remote
- Start date
- To be agreed
Six years of React in production
I have owned frontends outright, at Stellia.ai, Sweez and Leadbay, and joined existing teams at Suzuki France and Sciences Po, following their conventions and reviews.
Through jCode, I work with public institutions, established companies and startups. My own products, WorkoutGen and Ragmir, taught me what follows a release.
- of web development
- 10 years
- missions completed on Malt (November 2026)
- 80+
- as a freelancer
- 7 years
- from 47 client ratings on Malt (November 2026)
- 5.0/5
Other areas of expertise
What clients and colleagues say
“I strongly recommend working with JB. He was instrumental in getting our frontend off the ground, handling everything with zeal, unwavering dedication, and unparalleled reliability.”
LinkedIn“Jean-Baptiste nous a aidé dans le développement frontend de notre outil Sweez. C'est un développeur talentueux et hautement compétent. Son expertise technique et sa capacité à résoudre les problèmes de manière créative font de lui un atout précieux pour toute équipe de développement. Il est fiable, consciencieux et démontre une grande attention aux détails dans son travail. Il communique bien et est force de proposition. La qualité de son code et sa capacité d'adaptation sont remarquables.”
Malt“Jean-Baptiste Thery est une perle rare : à l'écoute, super pro, très réactif, disponible, créatif, perfectionniste, un des meilleurs développeurs que j'ai pu rencontrer dans toute ma carrière. Partir avec Jean Baptiste dans un projet, c'est l'assurance d'un travail parfait.”MaltLet's talk about your project.
Tell me what you want to build or improve, your budget and your target date.
- Fully remote
- English or French
- France · UK · US
Frequently asked questions
Which React versions do you work with?
React 19 on my recent projects, with Next.js 16 on the Sciences Po portal. On an existing application, I start from the version in place and its dependencies.
Can you take over an existing React codebase?
Yes. I review the code, dependencies and tests, then we agree priorities and an estimate before any change. The audit and recovery service starts with this review, at a fixed price.
Do you also build the backend?
Yes. I built WorkoutGen's Hono API on Cloudflare Workers and, with another developer, the Spring Boot 4 backend of the Sciences Po portal. I have also worked with Fastify, Symfony and PostgreSQL.
Do you use AI tools on React projects?
Yes, within each client's rules: same review, same tests, same CI. On my own product, WorkoutGen, I built the React 19 app with Claude Code, under architecture rules and human validation of sensitive changes. The agentic development page sets out my method.