OpenAPI schema customization in FastAPI

Introduction

OpenAPI schema customization lets you change how your API's description looks. This helps make your API easier to understand and use.

You want to add a title, version, or description to your API docs.

You need to add extra information like contact or license details.

You want to change the default URL where the docs appear.

You want to hide some endpoints from the docs.

You want to add tags or group endpoints for clarity.

Syntax

FastAPI

from fastapi import FastAPI

app = FastAPI(
    title="My API",
    description="This API does cool things.",
    version="1.0.0",
    contact={"name": "Support", "email": "[e-mail]"},
    license_info={"name": "MIT"},
    openapi_url="/custom_openapi.json",
    docs_url="/custom_docs"
)

You customize the schema by passing parameters when creating the FastAPI app.

openapi_url changes the JSON schema URL; docs_url changes the interactive docs URL.

Examples

Simple title and version change for your API docs.

FastAPI

app = FastAPI(title="Book Store API", version="2.0")

Adds a description and contact info to the docs.

FastAPI

app = FastAPI(
    description="API for managing tasks.",
    contact={"name": "Jane Doe", "email": "[e-mail]"}
)

Changes where the OpenAPI JSON and docs are served.

FastAPI

app = FastAPI(
    openapi_url="/api/schema.json",
    docs_url="/api/docs"
)

Sample Program

This example shows how to set title, description, version, contact, and license info. It also changes the OpenAPI and docs URLs. The endpoint '/hello' appears in docs with a tag. The '/hidden' endpoint is not shown in the docs.

FastAPI

from fastapi import FastAPI
from fastapi.responses import JSONResponse

app = FastAPI(
    title="Simple API",
    description="This API shows how to customize OpenAPI schema.",
    version="0.1",
    contact={"name": "API Support", "email": "[e-mail]"},
    license_info={"name": "Apache 2.0"},
    openapi_url="/openapi.json",
    docs_url="/docs"
)

@app.get("/hello", tags=["Greetings"])
async def say_hello():
    return {"message": "Hello, world!"}

@app.get("/hidden", include_in_schema=False)
async def hidden_endpoint():
    return JSONResponse({"secret": "This is hidden from docs"})

Important Notes

Use include_in_schema=False to hide endpoints from docs.

Tags help organize endpoints in the docs.

Changing openapi_url and docs_url helps if you want custom paths for your API docs.

Summary

Customize your API docs by setting parameters in FastAPI app creation.

You can add info like title, version, description, contact, and license.

You can hide endpoints or change where docs appear.

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