What a junior backend developer should know

The mandatory minimum

A language at working level. Not "completed a course" but the ability to write a few hundred lines split into comprehensible parts.

How the web works. What a request and response are, what methods and status codes mean, what headers are, how the URL differs from the body. This comes up almost every time.

Databases. Confidently: selecting with conditions, sorting, joins, grouping. An understanding of what an index is and why.

Plus a sense of how to design a couple of related tables without stepping on the obvious rakes.

One framework. Whichever your local postings ask for. Be able to write a request handler, connect a database, return a response, handle an error.

Tooling. Version control, the command line, reading logs, debugging.

What gets learned on the job

• Containers and deployment — good to show, not critical at entry.
• Queues and background jobs.
• Caching.
• Security beyond the basics.
• Microservices. You definitely don't need those at entry.

What to show in a project

A service with the full path: request arrives, data validated, database consulted, response returned, event logged.

It helps if the following is visible:

• separation into layers — request handling apart from data access;
• input validation and comprehensible error messages;
• configuration outside the code, with no passwords in the repository;
• deployment — it opens behind a link.

A modest project, but it answers most interview questions.

Gaps that are visible immediately

Passwords and keys in the code. They open your repository, find a real key, and the conversation is over. Check your projects right now.

No error handling. A program that crashes on any unexpected input reads as coursework.

Database queries inside loops. The classic beginner's error: a loop over a hundred records issuing a hundred queries.

No idea what a transaction is. Asked often, especially where money or orders are involved.

Testing yourself

Build a service that accepts data, stores it and returns it with filtering. Deploy it. Give the link to someone who writes backend and ask them to tear it apart.

The comments you get are the list of what an interview will ask. Getting them before rather than during a conversation with an employer is cheap: usually it's enough to ask someone in a community, or to build the project alongside someone more experienced.