Swagger has become an essential tool for developers working with APIs. It simplifies the process of designing, building, documenting, and consuming RESTful web services. By providing a standardized way to describe APIs, Swagger enhances collaboration between frontend and backend teams and ensures that APIs are well-documented and easy to understand.
This article offers a curated selection of interview questions focused on Swagger. Reviewing these questions will help you gain a deeper understanding of Swagger’s capabilities and best practices, preparing you to discuss and demonstrate your expertise confidently in any technical interview setting.
Swagger Interview Questions and Answers
1. Describe the components of a Swagger specification file.
A Swagger specification file, also known as an OpenAPI specification, describes the structure and behavior of an API in JSON or YAML format. Key components include:
- Info: Metadata about the API, such as title, description, version, and contact information.
- Paths: Available endpoints and operations, including parameters, request bodies, and responses.
- Definitions: Data models used in the API, often for reusable components.
- Parameters: Path, query, header, and body parameters for API operations.
- Responses: Possible responses for each operation, including status codes and response bodies.
- Security: Security schemes like API keys and OAuth2, specifying required authentication for operations.
- Tags: Group related operations for better organization.
- ExternalDocs: Links to additional documentation.
2. Define a simple GET endpoint in a Swagger file.
A simple GET endpoint in a Swagger file can be defined as follows:
swagger: "2.0"
info:
version: "1.0.0"
title: "Simple API"
paths:
/example:
get:
summary: "Returns a simple message"
responses:
200:
description: "A successful response"
schema:
type: "string"
example: "Hello, world!"
3. Add query parameters to an endpoint.
To add query parameters to an endpoint, define them in the parameters section of the endpoint’s definition. Here’s an example:
paths:
/users:
get:
summary: Get a list of users
parameters:
- in: query
name: age
required: false
schema:
type: integer
description: Filter users by age
- in: query
name: status
required: false
schema:
type: string
description: Filter users by status
responses:
'200':
description: A list of users
content:
application/json:
schema:
type: array
items:
$ref: '#/components/schemas/User'
In this example, the /users endpoint has two optional query parameters: age and status.
4. Document request and response payloads in Swagger.
To document request and response payloads, define the schema for the request body and response body using the components section for reusable schemas:
openapi: 3.0.0
info:
title: Sample API
version: 1.0.0
paths:
/user:
post:
summary: Create a new user
requestBody:
content:
application/json:
schema:
$ref: '#/components/schemas/User'
responses:
'200':
description: User created successfully
content:
application/json:
schema:
$ref: '#/components/schemas/UserResponse'
components:
schemas:
User:
type: object
properties:
username:
type: string
email:
type: string
UserResponse:
type: object
properties:
id:
type: integer
username:
type: string
email:
type: string
5. Handle authentication and authorization in Swagger.
To handle authentication and authorization, define security schemes in your Swagger configuration file. Here’s an example using API key-based authentication:
swagger: "2.0"
info:
version: "1.0.0"
title: "API with Authentication"
securityDefinitions:
ApiKeyAuth:
type: "apiKey"
name: "Authorization"
in: "header"
security:
- ApiKeyAuth: []
paths:
/example:
get:
security:
- ApiKeyAuth: []
summary: "Example endpoint"
responses:
200:
description: "Successful response"
In this example, ApiKeyAuth is defined in securityDefinitions and applied globally.
6. Use Swagger UI to test APIs.
Swagger UI provides a user-friendly interface to test and document APIs. To use it:
- Access the Interface: Through a URL pointing to a JSON or YAML file describing the API.
- Explore Endpoints: View available endpoints with descriptions, HTTP methods, parameters, and responses.
- Test Endpoints: Input parameters and execute requests directly from the interface.
- Authentication: Input necessary credentials if required.
7. Generate client SDKs from a Swagger definition.
To generate client SDKs from a Swagger definition, use tools like Swagger Codegen or OpenAPI Generator. These tools take a Swagger file as input and produce client libraries in the desired language.
Example:
swagger-codegen generate -i swagger.yaml -l python -o ./python-client
In this example, the swagger-codegen tool generates a Python client SDK from swagger.yaml.
8. Define reusable components in Swagger.
In Swagger, reusable components are defined under the components section. This can include schemas, responses, parameters, examples, request bodies, headers, and security schemes. By defining these components once, you can reference them multiple times throughout your API documentation.
Example:
openapi: 3.0.0
info:
title: Sample API
version: 1.0.0
paths:
/users:
get:
summary: Get a list of users
responses:
'200':
description: A JSON array of user names
content:
application/json:
schema:
$ref: '#/components/schemas/UserList'
components:
schemas:
UserList:
type: array
items:
type: string
In this example, the UserList schema is defined under components and referenced in the response of the /users endpoint.
9. Handle file uploads in Swagger.
Handling file uploads involves defining an API endpoint that accepts a file as input using the multipart/form-data content type.
Example:
paths:
/upload:
post:
summary: Uploads a file
consumes:
- multipart/form-data
parameters:
- in: formData
name: file
type: file
required: true
description: The file to upload
responses:
200:
description: File uploaded successfully
In this example, the /upload endpoint accepts a POST request with a file parameter.
10. Document deprecated endpoints in Swagger.
To mark an endpoint as deprecated, use the deprecated field in the OpenAPI specification. This field is a boolean and should be set to true for deprecated endpoints.
Example:
paths:
/old-endpoint:
get:
summary: "Old endpoint"
deprecated: true
responses:
'200':
description: "Successful response"
11. Use Swagger Codegen for server stub generation.
Swagger Codegen allows developers to generate client libraries, server stubs, and other resources from an OpenAPI Specification. To use it for server stub generation:
1. Install the Swagger Codegen CLI.
2. Prepare your OpenAPI Specification file.
3. Run the Swagger Codegen command.
Example:
swagger-codegen generate -i your_api_spec.yaml -l python-flask -o ./generated_server
In this example:
-ispecifies the input file.-lspecifies the language/framework for the server stub.-ospecifies the output directory.
12. Handle polymorphism in Swagger definitions.
Polymorphism allows you to define a base model and extend it with sub-models using the allOf keyword and discriminator fields.
Example:
components:
schemas:
Pet:
type: object
required:
- petType
properties:
petType:
type: string
discriminator:
propertyName: petType
example:
petType: Dog
Dog:
allOf:
- $ref: '#/components/schemas/Pet'
- type: object
properties:
breed:
type: string
Cat:
allOf:
- $ref: '#/components/schemas/Pet'
- type: object
properties:
color:
type: string
In this example, Pet is the base model with a discriminator field petType. The Dog and Cat models extend Pet using allOf.
13. Handle error responses in Swagger.
Handling error responses involves defining them in the API specification, ensuring developers understand possible errors and how to handle them. Define error responses using the responses object within an API operation.
Example:
paths:
/users:
get:
summary: Get a list of users
responses:
'200':
description: A list of users
content:
application/json:
schema:
type: array
items:
$ref: '#/components/schemas/User'
'400':
description: Bad Request
content:
application/json:
schema:
$ref: '#/components/schemas/Error'
'500':
description: Internal Server Error
content:
application/json:
schema:
$ref: '#/components/schemas/Error'
components:
schemas:
User:
type: object
properties:
id:
type: integer
name:
type: string
Error:
type: object
properties:
code:
type: integer
message:
type: string
In this example, the /users endpoint defines responses for both successful and error scenarios.
14. Document nested objects in Swagger.
To document nested objects, define the nested structure within the definitions section of your Swagger specification.
Example:
swagger: '2.0'
info:
version: 1.0.0
title: Nested Objects API
paths:
/example:
get:
summary: Example endpoint
responses:
200:
description: Successful response
schema:
$ref: '#/definitions/ParentObject'
definitions:
ParentObject:
type: object
properties:
id:
type: integer
name:
type: string
child:
$ref: '#/definitions/ChildObject'
ChildObject:
type: object
properties:
childId:
type: integer
childName:
type: string
In this example, ParentObject contains a nested ChildObject.
15. Use Swagger to generate API documentation automatically.
To generate API documentation automatically using Swagger, integrate it into your project. Here’s an example using Flask:
from flask import Flask
from flask_restful import Api, Resource
from flasgger import Swagger
app = Flask(__name__)
api = Api(app)
swagger = Swagger(app)
class HelloWorld(Resource):
def get(self):
"""
A simple GET endpoint
---
responses:
200:
description: A successful response
"""
return {'hello': 'world'}
api.add_resource(HelloWorld, '/')
if __name__ == '__main__':
app.run(debug=True)
In this example, the flasgger library integrates Swagger with a Flask application, and a simple API endpoint is defined with Swagger annotations.