Automatic API documentation (Swagger UI) in FastAPI - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is Swagger UI in the context of FastAPI?

Swagger UI is a tool that automatically generates interactive API documentation for your FastAPI application. It lets you see and test API endpoints in a web browser.

beginner

How does FastAPI provide automatic API documentation?

FastAPI uses the OpenAPI standard and automatically generates docs using Swagger UI and ReDoc without extra setup. It reads your code and creates interactive docs.

beginner

Which URL path shows the Swagger UI documentation by default in a FastAPI app?

By default, Swagger UI is available at the path '/docs' in a FastAPI application.

intermediate

How can you customize the title and description shown in Swagger UI in FastAPI?

You can customize the title and description by passing parameters like 'title' and 'description' when creating the FastAPI app instance.

beginner

What is the benefit of having automatic API documentation with Swagger UI?

It helps developers and users understand and test the API easily without writing separate docs. It saves time and reduces errors by showing live API info.

Where can you access Swagger UI documentation in a default FastAPI app?

A /swagger

B /api-docs

C /docs

D /documentation

FastAPI serves Swagger UI automatically at the '/docs' path by default.

Which standard does FastAPI use to generate API docs?

A OpenAPI

B SOAP

C GraphQL

D REST

FastAPI uses the OpenAPI standard to create automatic API documentation.

How do you change the title shown in Swagger UI for a FastAPI app?

A Set 'title' parameter in FastAPI() constructor

B Edit swagger.json file manually

C Change the HTML of Swagger UI

D Use a decorator on each endpoint

You customize the title by passing the 'title' argument when creating the FastAPI app instance.

What does Swagger UI allow you to do with your API?

A Deploy the API to a server

B View and test API endpoints interactively

C Compile the API code

D Encrypt API requests

Swagger UI provides an interactive interface to view and test API endpoints.

Which of these is NOT a feature of FastAPI's automatic docs?

A Interactive API testing

B Automatic endpoint listing

C Customizable metadata like title

D Manual writing of docs required

FastAPI generates docs automatically; manual writing is not required.

Explain how FastAPI generates automatic API documentation using Swagger UI.

Think about how FastAPI reads your code and creates docs you can use in a browser.

Describe the benefits of using Swagger UI for API documentation in FastAPI projects.

Consider how having live docs helps everyone working with the API.

Practice

1. What is the default URL path where FastAPI serves the automatic API documentation using Swagger UI?

easy

A. /docs

B. /swagger

C. /api-docs

D. /documentation

Solution

1. Step 1: Understand FastAPI default docs path

   FastAPI automatically provides Swagger UI documentation at the path '/docs' by default.

2. Step 2: Compare options with default path

   Among the options, only '/docs' matches the default URL for Swagger UI in FastAPI.

3. Final Answer:

   /docs -> Option A

4. Quick Check:

   Default Swagger UI docs path = /docs [OK]

Hint: Remember: FastAPI docs are at /docs by default [OK]

Common Mistakes:

• Confusing /swagger with /docs
• Assuming /api-docs is default
• Thinking documentation is at root /

2. Which of the following code snippets correctly imports and creates a FastAPI app that will have automatic Swagger UI documentation?

easy

A. import fastapi
app = fastapi.App()

B. from fastapi import API
app = API()

C. from fastapi import FastAPI
app = FastAPI()

D. import FastAPI
app = FastAPI()

Solution

1. Step 1: Check correct import and app creation

   The correct import is 'from fastapi import FastAPI' and app is created by calling FastAPI().

2. Step 2: Validate each option

   from fastapi import FastAPI app = FastAPI() matches the correct syntax. Options A, C, and D have wrong imports or class names.

3. Final Answer:

   from fastapi import FastAPI\napp = FastAPI() -> Option C

4. Quick Check:

   Correct import and app creation = from fastapi import FastAPI app = FastAPI() [OK]

Hint: FastAPI app is created by FastAPI() after correct import [OK]

Common Mistakes:

• Using wrong import names like API or App
• Trying to import FastAPI with capital letter as module
• Calling wrong constructor names

3. Given this FastAPI code snippet, what will you see when you open http://localhost:8000/docs in your browser?

from fastapi import FastAPI
app = FastAPI()

@app.get("/hello")
def say_hello():
    return {"message": "Hello, world!"}

medium

A. A 404 Not Found error because /docs is not defined

B. A plain JSON response with {"message": "Hello, world!"}

C. A blank page with no content

D. An interactive Swagger UI showing the /hello GET endpoint with a Try it out button

Solution

1. Step 1: Understand FastAPI automatic docs behavior

   FastAPI automatically generates Swagger UI at /docs showing all defined endpoints.

2. Step 2: Analyze the given code

   The code defines a GET endpoint /hello. The docs page will list this endpoint with interactive testing.

3. Final Answer:

   An interactive Swagger UI showing the /hello GET endpoint with a Try it out button -> Option D

4. Quick Check:

   FastAPI auto docs show endpoints interactively at /docs [OK]

Hint: Open /docs to see interactive API docs with all endpoints [OK]

Common Mistakes:

• Expecting JSON response at /docs instead of UI
• Thinking /docs must be manually coded
• Confusing /docs with endpoint paths

4. You wrote this FastAPI app but when you visit /docs, you get a 404 error. What is the likely cause?

from fastapi import FastAPI
app = FastAPI()

@app.get("/items")
def read_items():
    return [{"item_id": 1}]

# You run the app with: uvicorn main:app --port 8000 --host 0.0.0.0

# But /docs returns 404

medium

A. You are running the app with the wrong module or app name

B. The endpoint /items is missing

C. You need to add extra code to enable /docs

D. You forgot to import FastAPI

Solution

1. Step 1: Check the run command and app reference

   The command 'uvicorn main:app' requires a file named main.py with an app variable.

2. Step 2: Identify mismatch causing 404 on /docs

   If the file or app name is wrong, uvicorn won't serve the correct app, so /docs is missing.

3. Final Answer:

   You are running the app with the wrong module or app name -> Option A

4. Quick Check:

   Run command must match file and app names exactly [OK]

Hint: Match uvicorn run command module:app exactly [OK]

Common Mistakes:

• Assuming /docs needs manual enabling
• Forgetting to import FastAPI (but code shows import)
• Thinking missing endpoint causes /docs 404

5. You want to customize the automatic API docs path from the default /docs to /api-docs. Which FastAPI app creation code achieves this?

hard

A. app = FastAPI(swagger_ui_url="/api-docs")

B. app = FastAPI(docs_url="/api-docs")

C. app = FastAPI(openapi_url="/api-docs")

D. app = FastAPI(docs_path="/api-docs")

Solution

1. Step 1: Identify FastAPI parameter for docs path

   The parameter to change Swagger UI docs path is docs_url.

2. Step 2: Match option with correct parameter

   app = FastAPI(docs_url="/api-docs") uses docs_url="/api-docs", which correctly changes the docs path.

3. Final Answer:

   app = FastAPI(docs_url="/api-docs") -> Option B

4. Quick Check:

   Change docs path with docs_url parameter [OK]

Hint: Use docs_url to set custom docs path [OK]

Common Mistakes:

• Using swagger_ui_url which changes UI assets path
• Changing openapi_url affects JSON schema, not docs UI
• Using docs_path which is not a valid parameter