Feature-Sliced Design: A Modern and Methodical Frontend Architecture

Modern frontend application development is characterized by increasing complexity: multiplication of features, expanding development teams, and emergence of applications containing hundreds of interactive components. The absence of a structured architecture can quickly lead to degradation of maintainability and code quality.

In this context, Feature-Sliced Design (FSD) emerges as an architectural methodology specifically designed for organizing complex frontend projects. This approach provides a structured response to the scalability and maintainability challenges inherent in modern development.

This analysis examines the fundamental principles of FSD, its organizational structure, operational advantages and limitations, accompanied by visual representations to facilitate architectural understanding. This study continues analyses on development best practices, notably Conventional Commits and Conventional Comments.

Why a New Architecture for Frontend? 🤷‍️

Before detailing what FSD is, let’s start by asking a key question: what problem are we trying to solve?

Limitations of “Classic” Architectures

Classic approaches to structuring a frontend application (like the now famous organization by folders: components/, utils/, pages/) work well for small projects. But as soon as an application becomes larger or a team grows, these practices show their limits:

• Overloaded components and files that mix everything (a modal that’s half component… half business logic).
• Little consistency in the file tree: each developer organizes “their way”.
• Many cross-dependencies → refactoring and testing become slow and risky.
• Difficult for a new developer to understand the project quickly.

The Need for a Scalable Structure

When an application needs to evolve rapidly or is maintained by several developers, a modular and well-thought-out structure becomes essential:

• Each part of the code must be clearly isolated.
• Maintenance must be simpler and localized (a modification should not break another module).
• Navigation in the project must be intuitive, even for newcomers.

Feature-Sliced Design addresses these issues by proposing an organization oriented on features and a clear arrangement by hierarchical layers.

Feature-Sliced Design: What Is It? 🤔

Feature-Sliced Design (FSD) is a frontend architecture based on two main principles:

1. Divide the application according to its features:
   • Each feature uses an autonomous and independent structure, containing everything necessary (components, business logic, API calls, styles…).
2. Structure features in hierarchical layers:
   • These layers clearly organize responsibilities (UI, business models, shared logic…) to define strict dependencies and avoid chaos.

The idea? Build a scalable, modular and evolutive architecture.

Feature-Sliced Design Structure

One of FSD’s strengths is its clear methodology for structuring a project. Here’s how it works.

1. Division by Features

Unlike traditional organization by file types (e.g., components/, pages/), FSD divides your application by features.

Example: An E-commerce App

Let’s imagine an e-commerce application. Instead of organizing your components by their type, here’s what modules look like with FSD:

/features
  /cart
      ├── ui/           → Cart-related components (CartButton, CartSummary)
      ├── model/        → State management (Redux slice, Zustand store, etc.)
      ├── lib/          → Cart-specific utility functions
      ├── hooks.ts      → Cart-specific hooks
  /product
      ├── ui/           → Product components (ProductCard, ProductDetails)
      ├── model/        → Product API, product state management
      ├── productApi.ts

• Cart Feature: Encompasses all logic related to cart management.
• Product Feature: Manages logic and views specific to products.

Each feature is autonomous and encapsulated, making the code much simpler to test, modify and understand.

2. Organization in Layers

In addition to dividing an application by features, FSD defines a structure in hierarchical layers. These layers serve to clarify which part of the application can interact with another.

Here are the main layers defined by FSD:

1️⃣ App Layer

Global layer for everything that configures the application (routes, themes, global providers, wrappers…). Example: App.tsx, main routing.

2️⃣ Process Layer

Cross-cutting processes that involve several features. Examples:

• Global authentication (e.g., login/logout).
• Analytics tracking (Google Analytics, Mixpanel).

3️⃣ Page Layer

Pages associated with the main routes of the application. Example: CartPage for the /cart route.

4️⃣ Features Layer

Where the heart of the application lies: each complete autonomous feature has its own folder (as in the e-commerce example above).

5️⃣ Entity Layer

Groups business models reusable throughout the application. Example: User, Product, Order.

6️⃣ Shared Layer

Layer for shared and generic elements of the application. Reusable solutions at the app scale: Example: Button, Modal, or utils like fetchApi.

Diagrams to Visualize FSD

To understand this architecture well, a diagram is often useful. Here are some models to imagine or recreate with a tool like Excalidraw or Figma.

Layer Hierarchy

Think of the different layers as an inverted pyramid where each layer depends strictly on those below.

Advantages of Feature-Sliced Design

Here’s why FSD is gaining popularity, especially for complex projects:

1. Modularity

Each feature (for example: “cart”) is isolated. This means you can:

• Remove or replace a feature without disrupting the entire project.
• Facilitate reuse of features in other projects.

2. Readability

FSD proposes a clear and intuitive organization:

• It’s much easier for a developer to quickly locate a specific feature or file.
• With layers and logical division, everyone shares a common vision of the architecture.

3. Facilitated Maintenance

By limiting side effects through clearly defined dependencies between layers, unexpected bugs are considerably reduced. Refactoring is also simpler, as each part of the code is isolated in its domain.

4. Scalability

Even if your project becomes huge (or your team triples in size), the FSD architecture remains suitable:

• Features being isolated, developers can work on them in parallel.
• The hierarchical layer organization avoids “spaghetti effects”, where everything depends on everything.

5. Promotes Onboarding of New Developers

With a clear structure, a junior or new teammate can quickly understand where each part of the project is located. Add good documentation to the FSD organization, and your team gains productivity.

Limitations of Feature-Sliced Design ️

Not everything is perfect. Here are some challenges related to FSD:

1. Complex Implementation

Adopting FSD is not instantaneous. It requires:

• Architectural reflection work from the beginning of the project.
• Training teams in this method so they align on this structure.

If you try to adopt this methodology during a project (with legacy code), it may require tedious refactoring.

2. Not Always Suitable for Small Projects

For a prototype, small project, or MVP (minimum viable product), FSD can be over-engineered. In these cases, a simple and classic structure can often suffice.

3. Learning Curve

FSD might be a bit disconcerting for developers who are not used to thinking in terms of features or hierarchical layers. However, once mastered, it offers lasting clarity.

Conclusion

Feature-Sliced Design constitutes a structured architectural response to the challenges inherent in modern and complex frontend projects. Organization by features and implementation of hierarchical layers guarantee optimized modularity, reinforced maintainability, and scalability adapted to extended development teams.

The effectiveness of this methodology remains contextually dependent. FSD presents maximum relevance for complex or long-term projects, while its application may prove disproportionate for prototypes or small-scale projects.

Evaluating the opportunity to adopt Feature-Sliced Design requires analysis of project specificities and organizational constraints.

Complete Technical Resource: Feature-Sliced Design Documentation.