Marius Sergent,freelance web & mobile developer in Nantes
I build web and mobile applications out of Nantes, for companies and freelancers across western France who have a real problem to solve, not just a box to tick. From geotechnical drilling to property management, I work where code has to hold up in production, not just in a demo. Development, hosting, training: three trades, one person to talk to.
A craft builtin the field
I started with hardware before software. An electronics-focused technical baccalaureate, then a higher technical diploma in computing and networks for industry: in those years I learned to think close to the machine, where a mistake shows up on an oscilloscope. Software came next, and I settled into it for good, through a developer-designer degree and then a master's in software architecture. That move from hardware to software still shows up whenever a project needs code to talk to a sensor or run on a constrained device. I put all of it to work for clients from 2013 on, and the real learning kept happening in the field, one project at a time, well before I put a name on it.
Sergent.dev came in 2019. Not a career change, more the moment I fully committed to going independent and gave a name to what I was already doing: seeing projects through end to end, without subcontracting the hard parts, without diluting responsibility. More than eighty projects later, I'm still the same person sitting across from the client, from the first conversation to the production release.
Real projects,real constraints
Instead of lining up logos, here is what my projects really look like once you open the hood.
Prolog · Mobile field app
Prolog, built for Geosond, is the project I talk about most, because I'm allowed to. It's a React Native app running on a ruggedized Android tablet, set down next to a drilling rig, with no internet connection. It talks to a drilling probe over direct WiFi and runs an embedded machine learning model (LightGBM exported to ONNX) to classify the ground being drilled, in real time. Everything happens on the device: inference, storage, computation. No cloud, no server, no safety net. On a worksite, in the rain, wearing gloves, that's the kind of constraint that separates a demo from a tool that holds.
Property management platform
A property management platform, rebuilt around a headless CMS (Strapi) and a Next.js front end. The challenge wasn't the interface, it was how the data moved: syncing information that lived across several systems, giving each role (manager, owner) the right view without exposing everything, and keeping all of it maintainable. A decoupled architecture, clear data contracts, and one rule: if a piece of data has a source of truth, it has exactly one.
Hosting and deployment
Hosting and deploying what I build, because shipping the code is only half the job. Several apps and sites run on VPS machines I administer with Docker, behind a build-and-deploy pipeline I wired by hand on GitHub Actions. Nothing baroque: a push to the right branch, tests that pass, an image that builds, a deployment that happens on its own. When something breaks at 11pm, I know exactly where to look, because I laid every brick myself.
WordPress, PrestaShop & AI
And then there's everything around WordPress and PrestaShop, which plenty of developers look down on and which quietly keeps countless businesses running. I've even plugged AI into it to automate the tedious content chores. The right tool is the one that solves the client's problem, not the one that impresses my peers.
A blog fromthe field
I keep a blog, and I only write about things I've actually built. No copied tutorials, no trends commented on from a distance. When I write about running an ML model offline, it's because I fought with ONNX output formats on a real worksite. When I compare React Native and PWAs, it's after shipping both. If you want to judge my work before we even talk, that's probably the best place to start.
Method andprinciples
Spec before code
I don't touch a line until we agree on what we're building and why. It avoids the worst outcome: something technically flawless that doesn't answer the need.
The simplest thing that works
I'm wary of architectures that brace for problems you may never have. You can always add complexity later; unwinding it costs far more.
Fail loudly
Typed errors, validation as early as possible, never a bug swallowed in silence. An app that crashes clearly can be fixed; an app that lies about its state costs you days.
No nasty surprises
You always know where things stand, what's moving, what's stuck. I'd rather send an honest message flagging a delay than a silence that hides it.
Teaching tounderstand deeply
I also teach, in professional training with Sparks and in higher education at Sup de Vinci, to future web and mobile developers. I do it for a reason that's as selfish as it is generous: teaching forces you to really understand something, not roughly. Having to explain a concept to a beginner is the best test of whether you actually master it yourself. It keeps me honest about what I know, and about what I only think I know.
Theytrusted me
More than eighty projects delivered, twelve years in business, and a large majority of clients who come back or refer me. I work mostly by word of mouth, which is probably the most honest signal anyone can give about the quality of their work.
“Cela fait maintenant 8 ans que nous travaillons avec Marius, qui est un véritable soutien et un atout précieux dans la création et le suivi de projets. Peu importe le secteur, il s'implique pleinement dans votre domaine afin de vous proposer des solutions en parfaite adéquation avec vos attentes et votre budget. Merci à toi, cher partenaire. C'est un véritable plaisir de collaborer avec toi”
“Je ne peux que recommander Marius Sergent pour vos projets. C'est un professionnel sérieux, rigoureux et toujours attentif. C'est toujours un plaisir de collaborer à ses côtés, il challenge nos étudiants et les incite à se dépasser. Merci Marius !”
“Entreprise experte dans son domaine. Réactif, professionnel, toujours de bons conseils et très disponible. Je ne pourrais pas exercer mon activité aussi sereinement sans eux.”
“Très bon service, support et conseils depuis notre passage chez Marius, merci beaucoup !”
A project,a question?
Got a project, a still-fuzzy idea, or just a technical question that's keeping you stuck? Write to me. I reply fast, usually within 24 hours, and I'll tell you honestly whether I'm the right person to help, or not.