Development
React and Next.js development
React is a JavaScript library created by Meta to build user interfaces from reusable components. Combined with Next.js, it enables fast web applications, server-rendered for search engines, and rich interfaces that respond instantly to user actions.
Agencei develops with React and Next.js for product teams, software vendors and companies that need a demanding interface: complex dashboards, online editors, configurators, portals with many states and interactions. We also reinforce teams, take over React projects slowed down by technical debt or migrate legacy interfaces.
We deliver structured, tested TypeScript code, together with a design system when several applications must share the same visual identity.
When do we step in?
Building a rich, responsive interface
Your application requires complex interactions: instant filters, drag and drop, inline editing, real-time updates. React is designed for this type of interface.
Migrating a jQuery, Angular.js or server-rendered interface
Your front end relies on abandoned technologies or server-generated pages that are hard to evolve. We migrate progressively to React, screen by screen.
Setting up a design system
Several applications or teams reproduce the same components with variations. A shared React component library harmonizes the experience and speeds up development.
Taking over a slowed-down React project
Deliveries have slowed, every change breaks something else, performance is degrading. We audit the architecture, state management and tests, then clean up progressively.
Reinforcing your front-end team
You need experienced React developers to meet a deadline or level up your team, fitting into your methods and tools.
How we work
- 1
Audit or scoping
For an existing project, review of code, dependencies and performance. For a new project, definition of journeys, states and accessibility and SEO constraints.
- 2
Front-end architecture
Choice between React alone and Next.js, rendering strategy (client, server, static), state management, component organization, tooling and conventions.
- 3
Design system and components
Building base components (forms, tables, navigation) documented in Storybook, accessible and tested.
- 4
Screen development
Assembling components into screens, connecting to APIs, handling loading and error states, integration tests.
- 5
Performance and accessibility
Measuring Core Web Vitals, code splitting, rendering optimization, checking keyboard and screen reader accessibility.
- 6
Delivery and handover
Continuous integration pipeline, documentation and knowledge transfer to your team.
Technologies we use
- React
- Next.js
- TypeScript
- React Query
- Zustand or Redux Toolkit
- React Hook Form
- Tailwind CSS
- Storybook
- Vitest
- Playwright
- Vite
- Vercel
Related expertise
Why choose Agencei?
React in depth, not just on the surface
Server rendering, streaming, state management, memoization, accessibility: we know the internal mechanisms that make the difference on complex interfaces.
Components built to last
We favour simple, typed and documented components over clever abstractions that nobody will be able to maintain.
Performance verified on real devices
We measure load and interaction times on real devices and connections, not only on a development machine.
Integration with your teams
We adopt your conventions, code reviews and tools, whether we work as reinforcement or as an autonomous team.
In brief
- What is this service?
- Front-end development service with React and Next.js: rich web interfaces, server-rendered applications, design systems, migration and takeover of existing React projects, team reinforcement.
- Who is it for?
- Product teams, software vendors and companies that need a demanding web interface or want to modernize, clean up or speed up an existing front end.
- What problem does it solve?
- Delivering a fast, accessible and maintainable interface, and escaping blockers caused by obsolete front-end technologies or React technical debt.
- How long does it usually take?
- From a few weeks for a focused interface or an audit with an action plan, to several months for a complete application or a progressive migration.
- What factors influence the price?
- Number of screens and states, complexity of interactions, performance, accessibility and SEO requirements, condition of the existing code and the need for a design system.
- How does the engagement run?
- Audit or scoping, front-end architecture, design system and components, development of API-connected screens, performance and accessibility, delivery and handover.
- What are the risks?
- Over-engineered state management, poorly maintained dependencies, performance degraded by uncontrolled rendering, neglected accessibility, a migration that drags on without being broken down.
- What alternatives exist?
- Vue.js or Angular if your team already masters them, server-rendered pages with little JavaScript for a simple site, or a CMS with a theme if the interface is not a differentiator.
Frequently asked questions
What is the difference between React and Next.js?
React is the component library. Next.js is an application framework built on React that adds server-side rendering, static generation, routing and image and font optimization. Next.js is recommended for most public sites and applications; React alone is enough for an internal tool behind authentication.
Is React suitable for SEO?
A React application rendered only on the client can be poorly indexed. With Next.js, pages are server-rendered or pre-generated, which guarantees correct indexing and good load times.
Can you take over our existing React application?
Yes. We start with an audit of the architecture, dependencies, performance and tests, then propose a progressive clean-up plan compatible with ongoing deliveries.
Do we need a design system for a single project?
Not necessarily. A design system is justified when several applications or teams share components. For a single project, a well-organized component library is enough and can grow into a design system later.
Do you work as reinforcement for an in-house team?
Yes. We can integrate one or more React developers into your team, with your methods and tools, for a defined period or until a product deadline.
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See this serviceTell us about your project
Describe your need in a few lines: we come back to you with a first analysis and the next steps.