Hey! I’m Sergi Mitjavila,Fullstack Developer
Full Stack Developer with 6 years of experience, specialized in clean code and clean architecture. I work with .NET Core, React, Next.js, and TypeScript to build scalable products, from component architecture to API integration, always with a focus on performance and maintainable code.
Featured technical case studies
Image Processor
Free Next.js tool for converting image formats (PNG to WebP, etc.), reducing quality, and resizing, for a single image or in batch. I built it in my spare time after noticing that existing alternatives lock real functionality behind a paywall; I now use it regularly in my personal projects.
La Cullera
Recipe management app with user authentication, where each user saves and organizes their own recipes. It includes an automatic quantity recalculation system based on the number of servings, keeping every ingredient proportional. Built solo (backend and frontend) with Claude as a development copilot, and deployed on AWS.
My specialized ecosystem of tools & languages
Frontend
React.js
Next.js
Typescript
HTML
CSS
Styled Components
SASS
Linaria
Backend
.NET Core
C#
Entity Framework
Unit Testing
RES APIs
GraphQL
PostgreSQL
MongoDB
Tools
Visual Studio Code
GIT
Docker
Bitbucket
Jira
Github
Slack
Claude
Crafting high-performance digital architectures
Full Stack Developer with 6 years of experience in frontend and backend development, specialized in clean code and clean architecture to build scalable, easy-to-maintain products. Experienced with .NET Core, React, Next.js, TypeScript and PostgreSQL, working with microservices, REST APIs and Agile/Scrum.
My approach starts with thinking before building: clean code, decoupled architectures and good practices that let the product grow without piling up technical debt. I'm involved across the whole development cycle, from new features to performance optimization, accessibility and SEO, using tools like Docker and GA4 for monitoring and continuous improvement.
Currently Senior Full Stack Developer at GoStudent, building new acquisition and conversion projects while streamlining, automating and maintaining existing systems.
When I'm not coding, you'll find me in the mountains, in the snow or with a book in hand.
{"role": "Senior Fullstack","focus": "Clean code","mainStack": [".NET Core", "React.js", "Next.js"],"loves": ["Frontend", "Performance", "Reading", "Hiking"]}
Let's Work Together
I'm always open to discussing new projects, clean architecture consulting, or full-time opportunities. Drop me a line!