What’s the Best Way to Structure a FastAPI Backend With a React/Next.js Frontend in a Single Repository?

A common question when building full-stack is whether to keep the FastAPI back-end and the React or Next.js front-end in one repository or two. For most projects, especially solo or AI-assisted ones, a single repository is simpler, as long as it is structured well. A clean layout keeps the two halves separate but together, easy to build and reason about. Here is the best way to structure a FastAPI back-end with a React or Next.js front-end in one repo.

Why a single repository

Keeping both halves in one repo, a monorepo, has real advantages for a full-stack app. You version the whole project together, so a change spanning front-end and back-end is one coherent commit, and there is one place to clone, one history, and one setup. For a project built by one person or an agent, this simplicity outweighs the separation of two repos. A single repo keeps the front-end and back-end in step. It is the pragmatic default for full-stack building.

The top-level layout

The core of a good structure is a clear top-level split. A backend folder and a frontend folder at the repository root immediately signal where each half lives, keeping their code, dependencies, and config from tangling. Anyone, human or agent, can see the shape of the project at a glance. This simple two-folder division is the backbone of the layout. Everything else hangs off it. Two clearly named folders at the root are the foundation of a clean monorepo.

Inside the back-end folder

The backend folder holds a self-contained FastAPI application. Inside, you keep the app code, the API routes, the data models, the database logic, and the back-end’s own dependency file, so it could almost stand alone. Organizing the back-end internally, routes here, models there, keeps it maintainable as it grows. The folder is the back-end’s whole world. Keeping it self-contained means the back-end has everything it needs in one place. A well-organized back-end folder is half of a clean structure.

Inside the front-end folder

The frontend folder holds a complete React or Next.js application. It has its own package file, its components, its pages, and its build setup, entirely separate from the back-end’s Python world. This separation is natural since the two halves use different languages and tools, and a framework like React expects its own project structure. Keeping the front-end self-contained mirrors the back-end. The folder is the front-end’s world, cleanly apart from the server. Two self-contained halves make the repo easy to work in.

Shared configuration at the root

Some things belong at the repository root, above both folders. A top-level README, a gitignore, a Docker Compose file, and project-wide config sit at the root because they concern the whole project, not one half. Keeping shared, project-level files here and half-specific files inside each folder is the organizing principle. The root is for what spans both halves. This keeps the two folders focused while the whole project’s setup lives above them. Root for shared, folders for specific, is the rule.

How the halves connect

Structure aside, the halves connect through the API. The front-end calls the back-end’s endpoints over HTTP, so the two folders are linked not by shared code but by the API contract between them. Keeping that connection clean, the front-end knowing only the API, not the back-end’s internals, is what makes the separation work. The API is the seam between the folders. They live together but talk through a defined interface. That clean connection is what a good structure protects.

Keep concerns separate

The guiding principle is separation of concerns. The back-end handles data, logic, and security, the front-end handles presentation and interaction, and the structure should reflect that division rather than blurring it. Resisting the temptation to leak back-end logic into the front-end, or vice versa, keeps each half clean and independently changeable. The folder split enforces the conceptual split. Good structure makes the right thing easy and the wrong thing awkward. Separation of concerns is the deeper reason for the two-folder layout.

Manage dependencies per half

Each half manages its own dependencies. The back-end has its Python requirements and the front-end its package file, kept in their respective folders, so their toolchains never collide. This per-half dependency management is cleaner than trying to share one set across two different languages. Each folder installs and runs on its own terms. Keeping dependencies scoped to each half avoids a common source of confusion. Two independent dependency setups, one per folder, is the correct approach in a full-stack monorepo.

Running both halves

With this structure, you run each half from its folder, the back-end server from backend, the front-end dev server from frontend, and they talk over the API. During development you typically run both at once, and a root-level script or Docker Compose can start them together for convenience. The layout makes running the pair straightforward. Each half launches from its own home. A structure that makes both halves easy to start is a structure that supports daily development well. Clear folders make running simple.

Dockerizing the layout

This structure also dockerizes cleanly. Each half can have its own Dockerfile in its folder, and a root Docker Compose file can build and run both together, giving you a reproducible full-stack environment. The clean separation is exactly what makes containerizing straightforward, and it lets an agent that follows your Copilot project setup build and run the whole thing consistently. A well-structured repo is a well-dockerizable one. The layout that keeps the halves clean also makes them easy to containerize together.

The takeaway

The best way to structure a FastAPI back-end with a React or Next.js front-end in one repository is a clear monorepo: a backend folder and a frontend folder at the root, each self-contained with its own code, dependencies, and config, and shared project-level files like the README, gitignore, and Docker Compose at the root. The two halves stay cleanly separate, connected only through the API contract, which keeps concerns divided and each side independently changeable. This layout runs and dockerizes cleanly, and it is exactly the kind of clear structure that lets an AI agent build across both halves without confusion. One repo, two focused folders, connected by an API, is the pragmatic full-stack standard.

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