Freelance API design and integration, from REST to MCP
I design APIs and build the interfaces that consume them, fully remote. I built WorkoutGen's Hono API and Ragmir's MCP server, and the Spring Boot backend of a Sciences Po portal with another developer.
APIs I designed or integrated
APIs I built for my own products and for Sciences Po, and client APIs I connected interfaces to, over REST, GraphQL and WebSocket.
API of a workout app in production
A Hono API on Cloudflare Workers with an isolated database per member, Better Auth sign-in and payment integration
Open-source agentic RAG for coding agents
One retrieval layer exposed three ways: a typed TypeScript API, a command line and an MCP server with read-only tools for coding agents
Sciences Po · Confidential project
Academic portal, both sides of the API
Both sides of the contract, with another developer: a Spring Boot 4 backend and the Next.js 16 frontend that consumes it, behind CAS sign-in
Dashboard for AI corpus analysis
A GraphQL API consumed through a Redux architecture, developed test first with Vitest and Cypress
National website and dealer-site platform
A React back office over a REST API, connections to Suzuki's internal APIs and a Google Maps dealer search with geolocation
API contracts that last
An API outlives the screen that first consumed it. What matters is the shape of the resources, what an error says, how a change is versioned without breaking a client, and what the documentation actually guarantees.
I work on both the design and the integration: a REST contract for a new service, an interface connected to an existing REST or GraphQL API, real-time channels when the screen must react as data arrives, or an MCP server that opens chosen functions to AI agents.
I have built APIs with Hono, Fastify, Spring Boot and Symfony, and adapt to Express, NestJS or Laravel when that is what your team runs.
Possible deliverables
- REST contract with validation and error handling
- GraphQL API integration in the consuming interface, with its state management
- WebSocket connection for screens that update as data arrives
- Integration of an existing or third-party API into your application
- MCP server that exposes chosen functions to AI agents
- 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
I design the APIs I also consume
Five years of connecting interfaces to client APIs, in REST and GraphQL, shape how I design my own: resources the interface actually needs, errors it can display and changes that do not break existing clients.
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 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“Nous avons collaboré sur le projet Suzuki France avec Jean-Baptiste, et ce fut une très bonne expérience. Toujours pertinent dans ses réflexions et à l'écoute, il sait mener les projets avec sérieux et rigueur. Il m'a aussi été d'une grande aide lors de la réalisation grâce à ses connaissances du projet mais aussi ses compétences techniques avancées. Je recommande chaudement JB, et lui souhaite une pleine réussite en tant que freelance.”
LinkedIn“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.”LinkedInLet'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
REST or GraphQL for a new service?
It depends on who consumes it: GraphQL suits an interface that needs varied shapes of the same data, REST a stable contract used by several clients. I have designed REST APIs and built interfaces on GraphQL ones.
Can you work on an API you did not design?
Yes. Most of my client work was on that side: Suzuki France's internal APIs and the Google Maps API, and the GraphQL APIs of Stellia.ai and Sweez.
Do you handle real-time data?
Yes. The Sweez meeting assistant surfaces key information while the meeting is under way, over a WebSocket channel between the interface and the AI services.
Can AI agents use our API?
Yes. An MCP server can expose chosen functions of your API to AI agents. I designed and built Ragmir's, published on npm, which gave Claude Code and Codex cited project context. The MCP server service sets out what I build.