Senior Full-Stack Engineer

Senior Full-Stack Engineer

Bruxelles, Brussels, Belgium

€

6000 - 8500

32 - 40 hours

Build software differently with AI at the core

Software engineering is changing. At HeadFirst x Impellam, we are building an AI-native engineering organization where AI is becoming an integral part of how we design, build, test, and improve software.

As a Senior Full Stack Engineer, you will work across our .NET and Angular platforms and take ownership of complex features from technical design through to production.

You will still be the engineer responsible for what goes into production. The difference lies in how you get there. Tools such as Claude Code and Cursor help you investigate problems, write code, test ideas, refactor, and document solutions more quickly. Your job is to provide these tools with the right context, evaluate their output, and ensure that the final solution is secure, maintainable, and fit for purpose.

If that sounds more exciting than spending your days manually writing every line of code, keep reading.

What you will do

You will work across the entire stack and take ownership of the solutions you build.

Your responsibilities will include:

• Building end-to-end features using C#, .NET, ASP.NET Core, Angular, and TypeScript.




• Using AI coding agents as part of your daily engineering workflow.




• Providing AI agents with clear context, constraints, and technical guidance so they can contribute effectively.




• Reviewing AI-generated code and challenging it where necessary in terms of architecture, security, performance, maintainability, and testability.




• Designing and developing APIs, domain logic, data access layers, and integrations.




• Building user-facing experiences in collaboration with Product and Design.




• Improving existing code and reducing technical debt as part of the normal development process.




• Writing meaningful unit, integration, and end-to-end tests.




• Contributing to architectural decisions regarding scalability, reliability, and expansion into multiple markets.




• Sharing knowledge and helping the broader engineering team improve their skills in working with AI.

What does "senior" mean in this context?

For us, seniority isn't about how fast you can type or how much code you can write.

It's a matter of judgment.

You know how to examine a solution and ask the right questions:

• Does this fit the architecture?


• Are the assumptions actually correct?


• Is the security model sound?


• Will we still be able to keep this up in two years?


• Do the tests verify the correct behavior?


• Is there a simpler way to solve the problem?


• Did we provide the AI agent with enough context to make a good decision?

Whether you wrote the code yourself or an AI agent handled most of the implementation, you remain responsible for the result.

Here’s what we offer you

• Salary that matches your experience


• You will receive a salary range that matches your knowledge and experience. We reward you fairly for your commitment and development.


• Vacation pay and days off


• You will receive 8.33% vacation pay and are entitled to 27 vacation days per year based on full-time employment. This gives you plenty of time to recharge your batteries.


• Hybrid working


• We support hybrid working and apply a 60/40 split, whereby full-time employees spend three days at the office and two days working from home.


• Premium‑free pension


• We pay your entire pension premium. This means you accrue pension without having to contribute to it yourself. As a result, you are left with a higher net salary.


• Performance bonus


• Depending on your performance and that of HeadFirst Group, you may receive an annual bonus of one or two months' salary.


• Monthly extras


• You will receive a monthly allowance for internet, a vitality budget, a contribution towards lunch, and support in setting up your home office.

What we expect from you

Who You Are

You are an experienced engineer who enjoys solving complex problems and is committed to building things the right way.

You probably recognize yourself in the following:

• You have 7+ years of professional software engineering experience.


• You have extensive experience with C#, .NET, and ASP.NET Core.


• You have recent hands‑on experience with Angular and TypeScript.


• You are comfortable working with Entity Framework Core and relational databases.


• You have experience designing secure and maintainable REST APIs.


• Testing is a normal part of your workflow, not something added at the end.


• You have experience building and running cloud‑based applications.


• You are a skilled debugger and enjoy getting to the root of a problem.


• You can quickly get a handle on an existing codebase and start making a meaningful contribution.


• You are comfortable challenging technical decisions when you believe there is a better solution.


• You actively use AI coding tools such as Claude Code, Cursor, GitHub Copilot, or similar tools in your day‑to‑day work.

Our Technology

We will work with a modern Microsoft and Azure-based technology stack:

Backend: C#, .NET 9+, ASP.NET Core, Entity Framework Core, REST APIs

Frontend: Angular 20+, TypeScript

Testing: NUnit, Cypress

Cloud: Azure App Services, Container Apps, Functions, Cosmos DB, Azure SQL

Infrastructure: Docker, Docker Compose

CI/CD: Azure DevOps Pipelines, GitHub Actions

AI development: Claude Code, Cursor

Experience with Domain‑Driven Design, CQRS, distributed systems, or event‑driven architecture is a plus. So is experience with multi‑region or regulated platforms and Azure services such as App Configuration.

We are also interested in engineers who have considered how to work effectively with AI agents, for example by structuring specifications, documentation, prompts, or reusable context.

Why this role?

This is an opportunity to be part of an engineering organization that is actively changing the way software is built.

You’ll gain the technical expertise of a modern .NET and Angular environment, combined with the opportunity to work differently through AI‑assisted engineering. Rather than replacing engineering judgment, AI gives you more time to focus on architecture, problem‑solving, and building the right solution.

You will have real ownership of what you build, work closely with Product and Design, and help shape how the broader engineering team adopts agentic software development.

If you want to spend less time manually writing code and more time thinking about what should be built, why it should be built, and whether it's actually the right solution, this could be a great fit.

Because when an AI agent provides you with a polished implementation, the first question shouldn't be, “Does it compile?”

It should be: “Is this the right solution?”

YOUR BENEFITS AT HEADFIRST GROUP

27 vacation days

AND the possibility of adding or selling days. We work hard, but don't forget to relax.

Moments of celebration

With more than 450 colleagues, we always have something to celebrate. As one team, we celebrate birthdays, anniversaries and other successes!

OpenUp & HeadFirst Group Academy

Work on your mental health with access to the platform OpenUp. We learn every day, which is why we offer you free trainings and courses to keep developing yourself.

Bonus

Achieve your goals and see this reflected in the form of a bonus? That's possible with us! Hard work is rewarded.

Hybrid working

Work at one of our 4 locations, at home, or anywhere you feel comfortable. Of course you will receive a mobility and home working allowance from us.

Our headquarters

Take advantage of the free sports facilities, fine workstations and enjoy a delicious lunch buffet. A formidable competitor at home!

Meet a colleague

Erix Santman

Product Manager

Diederick van Tellingen

UX Designer

Mattijs Wassenburg

Managing Director

Christine Koekkoek

Product Owner

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