OpenAPI schema customization in FastAPI - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of customizing the OpenAPI schema in FastAPI?

Customizing the OpenAPI schema in FastAPI helps you change how your API documentation looks and behaves. It lets you add extra information, change titles, descriptions, or even add security details to make the docs clearer and more useful.

beginner

How do you change the title and description of the OpenAPI docs in FastAPI?

You can set the title and description by passing parameters like title and description when creating the FastAPI app, for example: FastAPI(title="My API", description="This API does cool things").

intermediate

What method do you override to fully customize the OpenAPI schema in FastAPI?

You override the app.openapi() method. This method returns the OpenAPI schema as a dictionary. You can modify this dictionary to add or change any part of the schema before returning it.

intermediate

How can you add a custom logo or contact information to your FastAPI OpenAPI docs?

You add these details inside the openapi schema dictionary under the 'info' key. For example, you can add a 'contact' field with name and email, or add 'x-logo' with a URL to your logo image.

intermediate

Why might you want to customize the OpenAPI schema's security definitions in FastAPI?

Customizing security definitions lets you describe how your API handles authentication, like API keys or OAuth. This helps users understand how to securely access your API and enables interactive docs to support login flows.

How do you set a custom title for your FastAPI OpenAPI docs?

A Pass title parameter when creating FastAPI app

B Edit the openapi.json file manually

C Use a decorator on each route

D Change the server settings

You set the title by passing the title parameter when creating the FastAPI app, like FastAPI(title="My API").

Which method do you override to customize the entire OpenAPI schema in FastAPI?

A app.run()

B app.schema()

C app.get_openapi()

D app.openapi()

The app.openapi() method returns the OpenAPI schema dictionary and can be overridden to customize the schema.

Where do you add contact information in the OpenAPI schema?

A In the 'servers' list

B Inside the 'paths' key

C Under the 'info' key

D In the 'components' section

Contact information is added under the 'info' key in the OpenAPI schema.

What is a benefit of customizing security schemes in OpenAPI docs?

A Helps users understand how to authenticate

B Changes the API response format

C Improves database performance

D Automatically fixes bugs

Custom security schemes help users know how to authenticate to your API.

Which of these is NOT a way to customize OpenAPI docs in FastAPI?

A Overriding the app.openapi() method

B Changing the Python version

C Editing the OpenAPI schema dictionary

D Passing parameters like title and description when creating the app

Changing the Python version does not customize OpenAPI docs.

Explain how to customize the OpenAPI schema in FastAPI to add a custom title, description, and contact info.

Think about parameters at app creation and modifying the schema dictionary.

Describe why and how you would add security schemes to your FastAPI OpenAPI documentation.

Focus on authentication and user guidance in docs.

Practice

1. What is the main purpose of customizing the OpenAPI schema in a FastAPI application?

easy

A. To provide clear API documentation with custom titles, descriptions, and versions

B. To speed up the API response time

C. To change the database connection settings

D. To automatically generate frontend UI components

Solution

1. Step 1: Understand OpenAPI schema role

   The OpenAPI schema defines how the API is documented and described for users and tools.

2. Step 2: Identify customization benefits

   Customizing it lets you add titles, descriptions, versions, and contact info to make docs clearer.

3. Final Answer:

   To provide clear API documentation with custom titles, descriptions, and versions -> Option A

4. Quick Check:

   OpenAPI schema customization = clear docs [OK]

Hint: Think: OpenAPI schema = API documentation details [OK]

Common Mistakes:

• Confusing schema customization with performance tuning
• Thinking it changes database or backend logic
• Assuming it auto-generates frontend code

2. Which of the following is the correct way to set a custom title and version for your FastAPI app's OpenAPI schema?

easy

A. app = FastAPI(schema_title="My API", schema_version="1.0.0")

B. app = FastAPI(openapi_title="My API", openapi_version="1.0.0")

C. app = FastAPI(title="My API", version="1.0.0")

D. app = FastAPI(api_title="My API", api_version="1.0.0")

Solution

1. Step 1: Recall FastAPI app parameters

   FastAPI accepts title and version as direct parameters in its constructor.

2. Step 2: Match correct parameter names

   The correct parameters are exactly title and version, not schema_title or openapi_title.

3. Final Answer:

   app = FastAPI(title="My API", version="1.0.0") -> Option C

4. Quick Check:

   FastAPI(title, version) = correct syntax [OK]

Hint: Use 'title' and 'version' directly in FastAPI() [OK]

Common Mistakes:

• Using incorrect parameter names like openapi_title
• Trying to set schema properties after app creation
• Confusing app config with route decorators

3. Given this FastAPI app code, what will be the OpenAPI docs URL by default?

from fastapi import FastAPI
app = FastAPI(title="Test API")

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

medium

A. /api-docs

B. /openapi.json

C. /swagger

D. /docs

Solution

1. Step 1: Recall FastAPI default docs path

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

2. Step 2: Differentiate docs and schema URLs

   /openapi.json is the raw schema JSON, not the interactive docs UI.

3. Final Answer:

   /docs -> Option D

4. Quick Check:

   Default docs URL = /docs [OK]

Hint: Swagger UI docs default path is /docs in FastAPI [OK]

Common Mistakes:

• Confusing /openapi.json with docs UI
• Assuming /swagger or /api-docs are default
• Not knowing FastAPI defaults for docs

4. What is wrong with this FastAPI app code if the goal is to hide the automatic docs UI?

app = FastAPI(docs_url=None)

@app.get("/users")
async def get_users():
    return [{"name": "Alice"}]

medium

A. docs_url should be set to False, not None

B. You must also set redoc_url=None to hide all docs

C. docs_url parameter does not exist in FastAPI

D. docs_url=None is correct and will hide docs UI

Solution

1. Step 1: Understand docs_url and redoc_url

   FastAPI has two docs UIs: Swagger UI at docs_url and ReDoc at redoc_url.

2. Step 2: Check hiding docs UI fully

   Setting docs_url=None hides Swagger UI but ReDoc remains unless redoc_url=None is also set.

3. Final Answer:

   You must also set redoc_url=None to hide all docs -> Option B

4. Quick Check:

   Hide all docs = docs_url=None + redoc_url=None [OK]

Hint: Set both docs_url and redoc_url to None to hide docs [OK]

Common Mistakes:

• Assuming docs_url=None hides all docs
• Using invalid values like False for docs_url
• Not knowing about ReDoc docs URL

5. You want to customize your FastAPI app's OpenAPI schema to include a contact email and license info. Which code snippet correctly achieves this?

hard

A. app = FastAPI(contact={"email": "[e-mail]"}, license_info={"name": "MIT"})

B. app = FastAPI(openapi_info={"contact": {"email": "[e-mail]"}, "license": {"name": "MIT"}})

C. app = FastAPI(openapi_contact={"email": "[e-mail]"}, openapi_license={"name": "MIT"})

D. app = FastAPI(openapi_contact_email="[e-mail]", openapi_license_name="MIT")

Solution

1. Step 1: Recall FastAPI parameters for contact and license

   FastAPI uses contact and license_info parameters to customize OpenAPI schema contact and license sections.

2. Step 2: Match correct parameter names and structure

   contact and license_info expect dictionaries with keys like email and name respectively.

3. Final Answer:

   app = FastAPI(contact={"email": "[e-mail]"}, license_info={"name": "MIT"}) -> Option A

4. Quick Check:

   Use contact and license_info dicts in FastAPI() [OK]

Hint: Use contact and license_info dicts in FastAPI() constructor [OK]

Common Mistakes:

• Using openapi_contact or openapi_license which are invalid
• Trying to nest contact inside openapi_info
• Passing strings instead of dicts for contact/license