Swagger Specification (OpenAPI Specification) Interview Questions and Answers
Master the OpenAPI Specification (formerly Swagger Specification) with the top 15 interview questions and answers. Learn OAS structure, paths, operations, components, schemas, parameters, responses, security, Spring Boot integration, and enterprise API design.
Introduction
The Swagger Specification, now known as the OpenAPI Specification (OAS), is the standard document used to describe REST APIs. It acts as a contract between API providers and API consumers by defining endpoints, request formats, response structures, authentication methods, reusable schemas, and server information.
Almost every modern enterprise uses the OpenAPI Specification to generate interactive documentation, SDKs, server stubs, API tests, and governance reports.
Interviewers commonly ask about OpenAPI document structure, Paths, Components, Schemas, Parameters, Responses, Security Schemes, and reusable definitions.
This guide covers the 15 most important Swagger Specification interview questions with production-ready explanations, Spring Boot examples, architecture diagrams, common mistakes, and interview follow-up questions.
What You'll Learn
After completing this guide, you'll be able to:
- Understand the OpenAPI Specification (OAS).
- Explain every major section of an OpenAPI document.
- Build reusable API specifications.
- Understand schemas, paths, parameters, and responses.
- Document authentication correctly.
- Answer OpenAPI interview questions confidently.
OpenAPI Specification Architecture
REST API
│
▼
OpenAPI Specification
│
┌───────────────┼────────────────┐
▼ ▼ ▼
Swagger UI Code Generator API Tests
│ │ │
└───────────────┼────────────────┘
▼
API Consumers
1. What is the Swagger Specification?
Short Answer
The Swagger Specification, now called the OpenAPI Specification (OAS), is a standard format for describing REST APIs.
It defines:
- API metadata
- Endpoints
- HTTP methods
- Parameters
- Request bodies
- Responses
- Authentication
- Data models
Why is it Important?
It provides a single source of truth for API design and documentation.
Interview Follow-up
Why was the Swagger Specification renamed?
Answer:
After donating the specification to the OpenAPI Initiative, it became the OpenAPI Specification (OAS).
2. What are the Main Sections of an OpenAPI Specification?
openapi:
info:
servers:
paths:
components:
security:
tags:
externalDocs:
Purpose
| Section | Purpose |
|---|---|
| openapi | OAS version |
| info | API information |
| servers | Base URLs |
| paths | API endpoints |
| components | Reusable definitions |
| security | Authentication |
| tags | Endpoint grouping |
3. What is the info Section?
The info object contains metadata about the API.
Example
info:
title: Employee API
version: 1.0.0
description: Employee Management System
Common Fields
- title
- version
- description
- contact
- license
- termsOfService
4. What is the servers Section?
The servers section defines where the API is hosted.
Example
servers:
- url: https://api.company.com
Multiple Servers
servers:
- url: https://dev.company.com
- url: https://qa.company.com
- url: https://api.company.com
Production Benefits
- Multiple environments
- Easy testing
- Environment switching
5. What is the paths Section?
The paths object defines every REST endpoint.
Example
paths:
/employees:
get:
post:
/employees/{id}:
get:
put:
delete:
Why is it Important?
It is the heart of the OpenAPI Specification.
6. What is an Operation Object?
An operation represents one HTTP method under a path.
Example
paths:
/employees:
get:
summary: Get Employees
post:
summary: Create Employee
Common Properties
- summary
- description
- parameters
- requestBody
- responses
- security
- tags
7. What are Components?
Components store reusable definitions.
Example
components:
schemas:
responses:
parameters:
securitySchemes:
Benefits
- Reusability
- Cleaner documentation
- Easier maintenance
- Reduced duplication
8. What are Schemas?
Schemas describe request and response models.
Example
Employee:
type: object
properties:
id:
type: integer
name:
type: string
Production Example
Employee
Customer
Order
Invoice
Payment
9. What are Parameters?
Parameters define input values supplied by the client.
Types
- Path
- Query
- Header
- Cookie
Example
parameters:
- name: id
in: path
required: true
schema:
type: integer
10. What is the Request Body?
The request body documents incoming payloads.
Example
requestBody:
required: true
content:
application/json:
Production Example
POST
PUT
PATCH APIs
11. What are Responses?
Responses describe all possible API outputs.
Example
responses:
"200":
description: Success
"404":
description: Employee Not Found
Best Practice
Document every possible response.
12. What are Security Schemes?
Security schemes describe authentication methods.
Example
components:
securitySchemes:
bearerAuth:
type: http
scheme: bearer
Common Types
- JWT
- OAuth2
- API Keys
- Basic Authentication
13. How Does Spring Boot Generate OpenAPI Specifications?
Using springdoc-openapi.
Dependency
<dependency>
<groupId>org.springdoc</groupId>
<artifactId>
springdoc-openapi-starter-webmvc-ui
</artifactId>
</dependency>
Flow
Spring Boot
↓
Annotations
↓
OpenAPI Specification
↓
Swagger UI
14. What are Common Swagger Specification Mistakes?
- Duplicate schemas
- Missing descriptions
- Undocumented responses
- Missing authentication
- Hardcoded server URLs
- No examples
- Poor endpoint names
- Ignoring reusable components
15. What are OpenAPI Specification Best Practices?
- Reuse components.
- Document every endpoint.
- Provide examples.
- Use meaningful summaries.
- Include all response codes.
- Document security.
- Keep version numbers updated.
- Avoid duplicate schemas.
- Group APIs using tags.
- Validate specifications before publishing.
OpenAPI Specification Summary
| Component | Purpose |
|---|---|
| openapi | Specification Version |
| info | Metadata |
| servers | Base URLs |
| paths | API Endpoints |
| operations | HTTP Methods |
| requestBody | Input Payload |
| responses | API Responses |
| schemas | Data Models |
| parameters | Client Inputs |
| securitySchemes | Authentication |
Interview Tips
When answering Swagger Specification interview questions:
- Explain that Swagger Specification is now called the OpenAPI Specification.
- Describe the purpose of each major section.
- Explain Paths and Operations.
- Discuss reusable Components.
- Explain Schemas and Request Bodies.
- Mention Security Schemes such as JWT and OAuth2.
- Explain Spring Boot integration with springdoc-openapi.
- Highlight how reusable components improve maintainability.
- Use practical enterprise examples.
- Mention that the specification serves as the API contract.
Key Takeaways
- The Swagger Specification evolved into the OpenAPI Specification (OAS) and is the industry standard for documenting REST APIs.
- An OpenAPI document acts as a contract between API providers and API consumers.
- The paths section defines API endpoints, while operations describe supported HTTP methods.
- Components enable reusable schemas, parameters, responses, and security definitions.
- Schemas document request and response models, improving consistency across APIs.
- Properly documenting request bodies, responses, and authentication improves developer experience.
- Spring Boot can automatically generate OpenAPI specifications using springdoc-openapi.
- A well-structured OpenAPI specification enables interactive documentation, SDK generation, automated testing, and API governance.
- Keeping the specification synchronized with the implementation is essential in enterprise environments.
- Mastering the OpenAPI Specification is a key skill for Java, Spring Boot, Microservices, REST API, and System Design interviews.