APIs are essential to modern software development, and choosing the right approach can impact everything from development speed to system performance. Two common paths in the Python ecosystem are RESTful API design and using FastAPI, a modern web framework.

In this post, we'll explore what each one means, how they differ, and when to use each.

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What is a RESTful API?

A RESTful API is an API that follows the architectural principles of REST (Representational State Transfer). It's not a specific tool or library, but a way of designing web services to be stateless, resource-based, and rely on standard HTTP methods.

Core REST Principles:

• Statelessness
• Use of standard HTTP verbs: GET, POST, PUT, DELETE
• URL endpoints represent resources (e.g., /users/123)
• Client-server separation
• Support for multiple formats like JSON and XML

Example (Conceptual REST):

Python
GET /users/123
Host: api.example.com

Response:
{
  "id": 123,
  "name": "Alice",
  "email": "alice@example.com"
}

You can implement RESTful APIs using frameworks like Flask, Django REST Framework, or Express.js (for JavaScript).

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What is FastAPI?

FastAPI is a modern, fast (high-performance) web framework for building APIs with Python 3.7+ based on standard Python type hints. It is designed to be easy to use, highly performant, and developer-friendly.

Why FastAPI stands out:

• Built on Starlette (web toolkit) and Pydantic (data validation)
• Native support for asynchronous programming (async/await)
• Auto-generates OpenAPI docs and Swagger UI
• Validates request/response data using Python types
• Offers fast JSON serialization and minimal overhead

Example (FastAPI code):

Python
from fastapi import FastAPI

app = FastAPI()

@app.get("/users/{user_id}")
async def read_user(user_id: int):
    return {"user_id": user_id}

When you visit /docs, FastAPI gives you interactive API documentation automatically.

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RESTful API vs FastAPI Comparison

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When Should You Use Each?

Use RESTful API (Design) if:

• You're working in a multi-language ecosystem.
• You need a design-agnostic structure.
• You're following existing company architecture guidelines.

Use FastAPI if:

• You're working with Python and want to move fast.
• You need high performance and async support.
• You want automatic docs and built-in validation.

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Conclusion

While RESTful APIs and FastAPI are often compared, they serve different purposes. RESTful API is a design paradigm, whereas FastAPI is a concrete implementation built for speed and developer efficiency.

If you're using Python and want a clean, performant, and scalable way to build APIs, FastAPI is one of the best choices available today. If you're designing APIs at a higher level or across multiple platforms, RESTful architecture provides a solid foundation.

Let your use case-and your stack-guide your decision.