What skills does a backend developer need?

Junior skills - build and change a working API

Pick one language and one framework: Python with FastAPI or Flask, Node.js with Express, or Go with net/http. Build REST endpoints that return the right status codes (200, 201, 400, 404, 500). Write SQL - SELECT, JOIN, GROUP BY, indexes - against PostgreSQL. Validate input, handle errors without crashing, and write basic tests with pytest or a similar tool. Use Git and read logs.

Mid-level skills - performance and correctness

Add authentication with sessions or JWT and store passwords with bcrypt. Speed up slow queries with indexes and EXPLAIN. Add a Redis cache with the cache-aside pattern. Use cursor pagination for large lists, rate limiting, idempotency keys for payments and retries, and timeouts on every outgoing HTTP call. Work with a message queue such as SQS or Kafka. Package the service in Docker.

Senior skills - systems that keep running

Plan zero-downtime schema migrations, design multi-tenant data isolation, and route reads to replicas. Handle distributed problems like race conditions and partial failures (sagas, retries with backoff). Add tracing with OpenTelemetry. Make design tradeoffs you can explain, for example when to cache and when not to.

How to show these skills to an employer

Employers ask "what did you build, and what went wrong?" Pick projects that answer it: an API with real JWT login, a cache that cut response time, a paginated endpoint that stays fast on a big table. Write each one up with the problem, what you changed and how you tested it, and put them on one portfolio page linked from your resume.

Real Backend work to put in your portfolio

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