The short answer
- Choose NestJS if your team works in TypeScript and Node.js and wants a framework that decides the architecture for you.
- Choose FastAPI if you want a light Python toolkit for typed, async APIs and are happy to decide the project structure yourself.
- Choose Austial if you want Python and FastAPI but with NestJS-style modules, controllers, providers and dependency injection, usually because the codebase or the team is growing.
NestJS, FastAPI and Austial side by side
The columns are not rivals on every row. FastAPI is a toolkit and Austial is a framework built on it, so most of the differences are about how much structure is decided for you.
| NestJS | FastAPI | Austial | |
|---|---|---|---|
| Language | TypeScript on Node.js | Python | Python 3.11 or newer |
| Built on | Express or Fastify | Starlette and Pydantic | FastAPI |
| Project structure | Modules, controllers and providers are prescribed | Up to you: routers and folders by convention | Modules, controllers and providers are prescribed |
| Dependency injection | Built-in container, constructor injection | Depends() on function parameters | Built-in container, constructor injection from type hints |
| Validation | Pipes with class-validator | Pydantic models | Pydantic models and a ValidationPipe |
| Request pipeline | Middleware, guards, interceptors, pipes, exception filters | Middleware and dependencies | Middleware, then guards, pipes, interceptors, handler, exception filters |
| API docs | Swagger module | OpenAPI and /docs built in | FastAPI's OpenAPI and /docs keep working |
| CLI | nest new and nest generate | fastapi dev and fastapi run, no code generator | austial new and austial generate |
| Testing | Test.createTestingModule() | TestClient with dependency overrides | Test.create_testing_module() with real dependency injection |
Dependency injection: Depends() vs the constructor
FastAPI injects dependencies as function parameters, each wired with Depends(). NestJS and Austial inject them into a class constructor, and the container resolves them from the type hints. The second style scales better when many handlers share the same services, because the wiring lives in one module instead of every route.
# FastAPI: dependencies are function parameters
@router.get("/cats/{cat_id}")
async def find_one(cat_id: int, service: CatsService = Depends(get_cats_service)):
return service.find_one(cat_id)
# Austial: dependencies are constructor parameters, resolved by type hint
@Controller("cats")
class CatsController:
def __init__(self, service: CatsService):
self.service = service
@Get(":id")
async def find_one(self, id: int):
return self.service.find_one(id)Frequently asked questions
Is FastAPI similar to NestJS?
They share some ideas, such as decorators and automatically generated OpenAPI documentation. But FastAPI is a minimal toolkit that leaves the project structure to you, while NestJS prescribes modules, controllers and providers.
Can I use NestJS patterns with FastAPI?
Yes. You can follow the patterns by hand with routers and Depends(), or use a framework such as Austial that adds NestJS-style modules, controllers, providers and guards on top of FastAPI.
Does Austial replace FastAPI?
No. Austial runs on FastAPI. Every route is registered as a real FastAPI APIRouter, so FastAPI's OpenAPI schema and the Swagger UI at /docs keep working.
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