Freelance Svelte and SvelteKit development
I build web applications with Svelte and SvelteKit, fully remote. For Sciences Po, I developed Khartis V3, the thematic mapping application its Cartography Lab designed, in SvelteKit and Svelte 5.
Svelte and SvelteKit projects I built
Three projects, three uses of Svelte: a complete SvelteKit application, Svelte islands inside Astro and components shared through a design system.
Sciences Po's thematic mapping tool
Researchers and journalists make thematic maps in one SvelteKit and Svelte 5 app that installs and keeps working offline. A complete rewrite designed by the Cartography Lab, which I developed
Mortgage simulation platform
The whole platform moved to Astro with Svelte, with technical SEO, a redesign and a Strapi CMS the business teams use on their own
Components for the Vitamin design system
Reusable Svelte components for the design system shared by all of the Decathlon group's e-commerce applications
Interfaces that stay fast as the data grows
I develop application interfaces, public sites and shared components with Svelte and SvelteKit, with the tests that keep a page predictable once real data arrives.
I adapt to the version and conventions your project already uses.
Fundamentals
- Runes
- Plain HTML and CSS
- Routing
- Data loading
- Server rendering
- Static generation
- Form actions
Possible deliverables
- SvelteKit application with routing, data loading and rendering strategy
- Svelte components documented in Storybook and reused across projects
- In-browser processing for datasets a server round trip would slow down
- Migration of an existing interface to Svelte or Astro
- Performance and SEO work, as in HelloPrêt's move to Astro
- 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
Four years of Svelte in production
From Decathlon's Vitamin components in 2022 to Khartis V3 in Svelte 5, I choose Svelte when performance and simple components matter, and I work within your stack when it is already in place.
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
“Jean-Baptiste a été très réactif et très organisé. Je recommande à 100% ses services.”
Malt“On top of being very up-to-date with all techs and stacks front, he is a very creative software engineer who will use his curiosity to try and offer the best solution possible for the problem, without sticking to his guns.”
LinkedIn“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
Do you work with Svelte 5 and runes?
Yes. Khartis V3 for Sciences Po was developed with Svelte 5. On an existing project, I start from the version in use.
Can Svelte coexist with our current framework?
Yes. Svelte components can live inside an Astro site or be published for another application, so a migration can happen page by page rather than all at once.
Can you handle large datasets in the browser?
Yes. Khartis processes its data entirely in the browser with DuckDB-WASM and Apache Arrow, so the interface stays responsive with large files and no server round trip.
Can you build a SvelteKit application from scratch?
Yes. For Sciences Po, I developed Khartis V3 in SvelteKit and Svelte 5, a complete rewrite designed by the school's Cartography Lab. The web application development service covers the path from an idea or a prototype to a product in production.