Development Basic

Backend

The part of an application that runs on the server: business logic, database management, authentication, data processing, and everything the user doesn't see directly.

Pronunciation

/ˈbæk.ɛnd/
"BAK-end"
Listen on: Forvo Cambridge

What is it

The backend (or “server side”) is the part of an application that runs on servers — not in the user’s browser. It’s invisible to the end user, but it’s where all the real logic happens:

  • Verifying whether a password is correct
  • Saving and retrieving data from the database
  • Processing a payment
  • Sending an email
  • Calculating prices or inventory

If software were a restaurant:

  • The frontend is the dining room, waiters, presentation
  • The backend is the kitchen: cooks, ingredients, recipes, storage room

Backend Responsibilities

AreaWhat it does
Business logicBusiness rules: discounts, validations, approval workflows
DatabaseCreate, read, update, delete data (CRUD)
AuthenticationVerify who you are (login, sessions, JWT tokens)
AuthorizationVerify what you can do (role-based permissions)
APIsExpose endpoints for frontend or third parties to consume
IntegrationsConnect to external systems: payments, email, SMS, ERPs
ProcessingCalculations, data transformation, report generation
SecurityValidate inputs, prevent SQL injection, encrypt sensitive data

Backend Technologies

Programming Languages

LanguageStrengthUsed in
Node.js (JavaScript)High concurrency, same language as frontendStartups, real-time APIs
PythonAI/ML, readability, data scienceAI-powered APIs, data analysis
Java / KotlinRobustness, enterprise ecosystemBanking, insurance, large corporations
C# (.NET)Microsoft ecosystem, performanceCompanies with Microsoft stack
GoPerformance, simplicityHigh-scale systems
PHPMaturity, cheap hostingWordPress, legacy e-commerce
  • Node.js: Express, NestJS, Fastify
  • Python: Django, FastAPI, Flask
  • Java: Spring Boot
  • C#: ASP.NET Core

Databases

TypeExamplesWhen to use
SQL (relational)PostgreSQL, MySQL, SQL ServerStructured data, complex relationships
NoSQL (document)MongoDB, DynamoDBFlexible data, high scale
In-memoryRedisCache, sessions, queues
ColumnarCassandraBig data, time series

How a Typical Request Works

User clicks "View my orders"
        ↓
Frontend sends: GET /api/orders (with JWT token)
        ↓
Backend verifies JWT → identifies the user
        ↓
Backend queries: SELECT * FROM orders WHERE user_id = 123
        ↓
Database returns the data
        ↓
Backend formats the response as JSON
        ↓
Frontend receives and displays the order list

Backend as a Service (BaaS)

For projects that don’t want to manage all this infrastructure, platforms offer pre-configured backends:

  • Supabase — PostgreSQL database + auth + automatic APIs
  • Firebase — Google’s backend suite: real-time DB, auth, hosting
  • AWS Amplify — serverless backend on AWS
  • PocketBase — open source backend in a single executable

Useful for MVPs and startups; for companies with complex logic, they typically fall short.

Why Backend Quality Matters

Backend quality determines:

Security: most security breaches occur in the backend (SQL injection, broken authentication, exposed data)

Performance: a poorly optimized backend makes the whole app slow, even if the frontend is perfect

Scalability: can the system handle 100 users or 100,000? The answer is in the backend

Data integrity: your company’s data is the most valuable asset — a backend without validations can corrupt it

  • [[Frontend]] - The visible counterpart that communicates with the backend via API
  • [[API]] - The contract the backend exposes to be consumed
  • [[REST]] - The most common design style for backend APIs
  • [[Docker]] - How the backend is deployed reproducibly
  • [[Microservices]] - Architecture where the backend is divided into specialized services

Additional Resources:

All terms