Backend Engineer
What the work looks like, the stacks behind the title, what each level means and the training that helps, then how interviews run and how to prepare for each step.
What a backend engineer actually does
The parts of a product users never see, and that decide whether it is fast, reliable and secure.
A backend engineer builds the services, APIs and data models behind a product. The code matters, and so do the choices around it: which data model to use, how two services talk to each other, what happens when traffic doubles or when a dependency fails.
Most backend engineers also look after what they build once it runs in production. They watch how their services behave, take part in an on-call rotation and fix incidents with the rest of the team.
More and more teams also work with AI coding tools such as Claude Code, Cursor or GitHub Copilot, and expect engineers to use them with judgment.
- Building a new API or service, and reviewing the code of other engineers
- A design discussion on a data model or on how two services should communicate
- Agreeing an API contract with the frontend and product teams
- Looking at monitoring, fixing a production issue or taking an on-call shift
- Time on performance, tests and technical debt
Many companies, from large tech groups to startups, hire their backend engineers under the title Software Engineer, sometimes followed by Backend in brackets.
Behind the broader title, the stack and the systems described in the job ad show where the work really sits: mostly backend, full‑stack or closer to the interface. On your CV and in interviews, describing the services and data you owned tells a company more than the title alone.
The same title, very different stacks
Most backend searches are defined first by the language and framework of the team, then by the ground every backend engineer shares.
What each level means in practice
Titles vary from one company to the next. What changes from one level to the next is the scope you own and the decisions you take.
- Delivers well-defined tasks with code review
- Learns the codebase, the tests and the tools
- Debugs with support from the team
- Owns features from design to production
- Designs small services and APIs
- Takes part in on-call and incident fixes
- Designs services and data models for the team
- Leads technical decisions and their trade‑offs
- Mentors other engineers and leads on incidents
- Sets technical direction across several teams
- Owns long-term architecture and standards
- Writes the design documents others build on
The paths into the role, and what really counts
Companies look first at what you have built and run in production. Education and certifications help most early in a career, or to change field.
- Engineering school or master's in computer scienceThe most common path in France, and often expected by large companies.
- University degree in computer scienceThe most common path in the US, at bachelor's or master's level.
- Bootcamp or self-taught, with real projectsAccepted more often by startups and product companies, with a portfolio or open source work to show.
- Moving from a nearby roleFrontend, QA automation or data engineers often move into backend work inside the same company.
Our view: a certification can open a door, and the conversation about what you built is what gets you hired.
A conversation with a senior tech recruiter
Your first interview is with one of our senior tech recruiters, who knows the role, the stacks and the levels in this guide. The conversation covers your own work through real examples, and the technical exercises come later, with the company. Before the call, we send you the six themes we will cover so you can prepare your examples.
- What you owned yourselfThe services, APIs or data models you were responsible for, and your own part in the team's work.
- Your environment and its constraintsTraffic, data volumes, legacy code, team size or regulation: what shaped your technical choices.
- The decisions you madeA design or technology choice, the options you compared and the reasons for the one you kept.
- The impact of your workWhat changed thanks to your work, with numbers when you have them: latency, costs, incidents or delivery speed.
- How you work with other teamsYour work with product, frontend, data or SRE teams, and how you settle a disagreement.
- What you want nextThe kind of systems, team and scope you are looking for in your next role.
- Systems you have owned in production
- Design trade‑offs you can explain
- Scale, performance and how you handle incidents
- How you work with product teams
The same ground for every candidate. For a given role, every candidate answers the same final questions, built with the hiring manager around what the role really needs.
Ready for the next steps. After our call, we tell you how the company runs its interviews, who you will meet at each step and what each step is meant to assess.
What the company will assess, step by step
Each company runs its own process, and we walk you through its steps before you start. Backend processes often combine the steps below, and the depth expected at each step grows with your level.
- A coding exerciseLive coding or a take-home on a realistic problem, such as an endpoint to build, a data processing task or a bug to fix.
- System designDesigning a service from a short brief: the requirements, the API, the data model, how it scales and how it fails.
- A deep dive on your past workOne system you built, discussed in depth: its architecture, your choices, its incidents and what you would change today.
- Meeting the manager and the teamHow you work, how you take decisions with others and what the team expects in your first months.
- ConfirmedYou cover the basics clearly, explain each component you bring in and follow the interviewer on the harder parts of the design.
- SeniorYou lead the discussion, go deep on two or three parts of the design and point out the limits of your own solution before you are asked.
- Staff and PrincipalYou run most of the interview as a peer, weigh the long-term consequences of each choice and connect the design to the rest of the organisation.
How to prepare as a backend engineer
Practical advice for each step of a backend process, from the way you introduce yourself to the questions you ask at the end of each interview.
Start with the systems you worked on, their scale and your part in them. Mention your stack in one sentence, then close with what you want next.
For each one, prepare the context, the constraints, your decision, the options you set aside, the result and what you would change today. Say "we" for the team and "I" for your own part.
Interviewers often ask about requests per second, data volumes, latency, error rates or release frequency. Orders of magnitude are enough, and they make your examples concrete.
In system design, ask about the users, the traffic and what matters most before you draw anything. Then explain each choice with its trade‑off, and say where your design would reach its limits.
Keep to the time suggested and add a short README with your choices, their trade‑offs and what you would add with more time. Clear tests and a clean structure count as much as the result.
Rules on AI coding assistants differ from one company to the next, and sometimes from one step to the next. Ask before each step, and when they are allowed, explain what you ask the tool and how you check its output.
- Walk us through a service you designed: the data model and the trade‑offs you made.
- How would you design an API for this feature, and how would it behave under ten times the traffic?
- Tell us about an incident you handled in production, and what changed afterwards.
- How do you test and deploy your code?
- Who owns the services I would work on, and who is on call?
- What happened after your last major incident?
- How often do you deploy to production, and how?
- How are architecture decisions taken and written down?
- How much time goes to technical debt?
- How does the team use AI coding tools day to day?
Where backend engineers come from, and where they go
The roles people most often hold before this one, and the ones they most often move to.
Some backend engineers also start in QA and test automation.