Beginner LevelREST APIs & Web Services
What is OpenAPI 3.0 (Swagger) and why is contract-first API design important?
❓ Interview Prompt: Explain OpenAPI 3.0 specification structure, YAML/JSON schemas, code generators, interactive docs (Swagger UI), and contract-first development.
The OpenAPI Specification (OAS 3.0) is a vendor-neutral standard for describing RESTful APIs:
Contract-First API Design:
Teams define the OpenAPI YAML/JSON contract before writing code:
1
Parallel Work: Frontend and backend teams work simultaneously using mock servers generated directly from OAS specs.
2
Automated SDK Generation: Generates strongly-typed client SDKs (TypeScript, Swift, Java) automatically.
3
Interactive Documentation: Renders interactive Swagger UI documentation.
Code Implementation Example
yaml
openapi: 3.0.3
info:
title: User Management API
version: 1.0.0
paths:
/users/{id}:
get:
summary: Get user by ID
parameters:
- name: id
in: path
required: true
schema:
type: string
responses:
'200':
description: Successful response💡OpenAPI 3.0 YAML contract definition for GET /users/{id}.
🎯 Interview Key Takeaway
Contract-first OpenAPI specs enable mock servers, SDK generation, and automated documentation before coding starts.
#OpenAPI#Swagger#Contract-First#Beginner
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