What is OpenAPI & Swagger?
💡 Concept Name
OpenAPI Specification & Swagger – OpenAPI is a standard format to describe RESTful APIs, while Swagger refers to the suite of tools that use this specification to help create, document, and test APIs.
📘 Quick Intro
The OpenAPI Specification (OAS) provides a machine-readable way to define REST API endpoints, request/response structures, and authentication methods. Swagger tools take this spec and generate interactive documentation, editors, and client/server SDKs, making API development smoother.
🧠 Analogy / Short Story
Think of OpenAPI as the architectural blueprint for a building—it maps out every room, door, and fixture. Swagger acts as the virtual 3D tour, allowing developers and users to explore the API’s design interactively before it's built.
🔧 Technical Explanation
-
✅ OpenAPI:
- Written in YAML or JSON, it describes API paths, operations, request/response schemas, and security schemes.
- Supports features like versioning, servers, and reusable components.
- Language- and platform-neutral, compatible with various tools (OAS 3.0+).
-
❌ Swagger Tools:
swagger-ui: Generates interactive, web-based API documentation from OpenAPI specs.swagger-editor: Browser-based editor with live validation for OpenAPI documents.swagger-codegen/openapi-generator: Generate client libraries and server stubs in multiple languages.
🎯 Purpose & Use Case
- ✅ Create and share API contracts among teams before coding starts.
- ✅ Automatically generate interactive documentation for easier testing and onboarding.
- ✅ Produce SDKs for multiple programming languages to speed up client development.
- ✅ Maintain consistency, version control, and compliance throughout API lifecycle.
💻 Real Code Example
// openapi-swagger.yaml
openapi: 3.0.1
info:
title: Sample API
version: 1.0.0
paths:
/users:
get:
summary: Retrieve a list of users
responses:
'200':
description: Successful response
content:
application/json:
schema:
type: array
items:
$ref: '#/components/schemas/User'
components:
schemas:
User:
type: object
properties:
id:
type: integer
name:
type: string
❓ Interview Q&A
Q1: What does OAS stand for?
A: OpenAPI Specification.
Q2: Which formats does OpenAPI support?
A: YAML and JSON.
Q3: What is swagger-ui?
A: A tool to generate interactive API docs from OpenAPI specs.
Q4: How is OpenAPI versioned?
A: Using the info.version field in the spec.
Q5: Which command generates client SDKs?
A: openapi-generator generate.
Q6: Can OpenAPI describe WebSocket APIs?
A: No, it focuses on RESTful HTTP APIs.
Q7: How do you secure endpoints?
A: By defining securitySchemes under components.
Q8: What does swagger-editor do?
A: Provides an in-browser editor with validation for OpenAPI specs.
Q9: How to add examples in OpenAPI?
A: Use the examples object inside responses or requests.
Q10: When were callbacks introduced?
A: In OpenAPI version 3.0.
📝 MCQs
Q1. Which keyword defines reusable schemas in OpenAPI?
- definitions
- components
- schemas
- models
Q2. What UI tool generates interactive API documentation?
- swagger-editor
- redoc
- swagger-ui
- postman
Q3. Where does OpenAPI metadata reside?
- metadata
- info
- details
- description
Q4. Which tool generates server stubs?
- swagger-codegen
- openapi-generator
- nswag
- autorest
Q5. How are path parameters specified?
- [param]
- {param}
- :param
- <param>
Q6. What HTTP methods does OpenAPI support?
- Only GET/POST
- All standard HTTP verbs
- Only CRUD
- None
Q7. Where are global security schemes defined?
- components
- security
- auth
- servers
Q8. What is the latest OpenAPI version?
- 2.0
- 3.0.1
- 3.1.0
- 4.0.0
Q9. Where do you define server URLs?
- paths
- servers
- components
- info
Q10. Which tag groups API operations?
- groups
- tags
- categories
- labels
💡 Bonus Insight
Redoc is a popular alternative renderer that supports features like code samples, deep linking, and powerful search, ideal for large API documentation portals.
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