OpenAPI schema customization in FastAPI - Mini Project: Build & Apply

OpenAPI Schema Customization with FastAPI

📖 Scenario: You are building a simple web API using FastAPI. You want to customize the OpenAPI schema to provide a clear title, description, and version for your API documentation. This helps users understand what your API does and its current version.

🎯 Goal: Create a FastAPI app with a customized OpenAPI schema that includes a specific title, description, and version.

📋 What You'll Learn

Create a FastAPI app instance

Set the OpenAPI schema title to 'Book Store API'

Set the OpenAPI schema description to 'API for managing books in a store'

Set the OpenAPI schema version to '1.0.0'

Add a simple GET endpoint at '/' returning a welcome message

💡 Why This Matters

🌍 Real World

Customizing the OpenAPI schema helps API users understand the purpose and version of your API clearly, improving developer experience and documentation quality.

💼 Career

Many backend developer roles require building and documenting APIs. Knowing how to customize OpenAPI schemas with FastAPI is a valuable skill for creating professional APIs.

1

Create a FastAPI app instance

Write code to import FastAPI from fastapi and create a FastAPI app instance called app.

FastAPI

from fastapi import FastAPI

# Create the FastAPI app instance
# Your code here

Hint

Use app = FastAPI() to create the app instance.

2

Customize OpenAPI schema with title, description, and version

Modify the FastAPI app creation to include title='Book Store API', description='API for managing books in a store', and version='1.0.0' as parameters.

FastAPI

from fastapi import FastAPI

# Create the FastAPI app with custom OpenAPI schema info
# Your code here

Hint

Pass title, description, and version as arguments to FastAPI().

3

Add a GET endpoint at '/' returning a welcome message

Add a GET endpoint using @app.get("/") that returns a dictionary with the key message and value 'Welcome to the Book Store API!'.

FastAPI

from fastapi import FastAPI

app = FastAPI(
    title='Book Store API',
    description='API for managing books in a store',
    version='1.0.0'
)

# Add a GET endpoint at '/' returning a welcome message
# Your code here

Hint

Use @app.get("/") decorator and define a function read_root that returns the dictionary.

4

Run the FastAPI app with customized OpenAPI schema

Add the code to run the FastAPI app using if __name__ == "__main__" block with import uvicorn and uvicorn.run(app, host="127.0.0.1", port=8000).

FastAPI

from fastapi import FastAPI

app = FastAPI(
    title='Book Store API',
    description='API for managing books in a store',
    version='1.0.0'
)

@app.get("/")
def read_root():
    return {"message": "Welcome to the Book Store API!"}

# Add code to run the app with uvicorn
# Your code here

Hint

Use the standard Python entry point check and call uvicorn.run() with the app and host/port.

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