Swagger vs Redoc in FastAPI: Key Differences and Usage

In FastAPI, Swagger UI and Redoc are two built-in API documentation interfaces. Swagger UI offers interactive API testing with a simple layout, while Redoc provides a cleaner, more detailed view focused on readability and navigation.

Quick Comparison

Here is a quick side-by-side comparison of Swagger UI and Redoc in FastAPI.

Feature	Swagger UI	Redoc
Default URL	/docs	/redoc
Interactivity	Supports try-it-out for API calls	No try-it-out, read-only docs
Layout Style	Compact, tabbed interface	Clean, single-page scrollable layout
Customization	Supports custom CSS and JS	Supports custom CSS, limited JS
Performance	Faster initial load	Better for large APIs with many endpoints
Focus	Developer testing and exploration	Documentation readability and navigation

Key Differences

Swagger UI is designed for interactive API exploration. It lets developers send requests directly from the docs, making it great for testing endpoints quickly. Its interface is compact and uses tabs to separate different API sections.

Redoc, on the other hand, focuses on presenting API documentation in a clean and readable format. It does not support sending requests from the UI but offers a smooth scrolling experience with a sidebar for easy navigation through large APIs.

Customization options differ: Swagger UI allows injecting custom JavaScript and CSS for deeper changes, while Redoc mainly supports CSS tweaks. For large APIs, Redoc often performs better and is preferred for user-facing documentation, whereas Swagger UI is favored for developer testing during development.

Code Comparison

This example shows how to enable Swagger UI in a FastAPI app (enabled by default at /docs):

python

from fastapi import FastAPI

app = FastAPI()

@app.get("/items/{item_id}")
async def read_item(item_id: int):
    return {"item_id": item_id, "name": "Sample Item"}

Output

Running this app and visiting http://localhost:8000/docs shows Swagger UI with interactive API docs.

Redoc Equivalent

To use Redoc in the same FastAPI app, it is enabled by default at /redoc. No extra code is needed beyond the basic app:

python

from fastapi import FastAPI

app = FastAPI()

@app.get("/items/{item_id}")
async def read_item(item_id: int):
    return {"item_id": item_id, "name": "Sample Item"}

Output

Running this app and visiting http://localhost:8000/redoc shows Redoc with clean, scrollable API documentation.

When to Use Which

Choose Swagger UI when you want to test API endpoints interactively during development or debugging. It is best for developers who want to try API calls directly from the docs.

Choose Redoc when you want to provide clean, user-friendly API documentation for consumers or teams who need easy navigation and readability without interactive testing.

Both are included by default in FastAPI, so you can offer both interfaces to suit different needs.

Key Takeaways

Swagger UI in FastAPI offers interactive API testing at /docs by default.

Redoc provides clean, readable API docs at /redoc without interactivity.

Use Swagger UI for developer testing and Redoc for user-friendly documentation.

Both are built-in and can be used together in FastAPI apps.

Customization is easier with Swagger UI for interactivity; Redoc excels in navigation.