Senior Backend Engineer (Node.js / NestJS) – Greenfield Product

Berlin, Germany

We are building a new standalone product from the ground up and are looking for a Senior Backend Engineer to help design and build the system's foundation.

In this role, you will play a key role inshaping the product's architecture, backend services, and technical direction . You will work closely with frontend engineers, product managers, and stakeholders to turn ideas into reliable, scalable backend systems.

This is an opportunity for engineers who enjoy designing systems, solving complex technical challenges, and taking ownership of meaningful projects from concept to production .

What You’ll Work On

Build and maintain scalable backend services using Node.js and NestJS

Design a clean system architecture for a new production product

Take ownership of features from concept through deployment

Define and implement APIs, services, and backend infrastructure

Collaborate with frontend engineers, product managers, and designers

Establish development standards, CI/CD pipelines, and engineering best practices

Mentor other engineers through code reviews and technical feedback

Continuously improve workflows using modern tooling and AI-assisted engineering

AI-Augmented Engineering

AI is part of how we work.

We expect engineers to actively use modern AI tools to improve development speed and quality , while maintaining strong engineering judgment.

You should be comfortable:

Using AI-assisted coding tools in your daily workflow

Writing effective prompts and critically evaluating AI output

Identifying AI limitations and failure modes

This role is for engineers who see AI as a tool to enhance engineering , not replace good engineering practices.

Your Skills

Must Have

5+ years of backend engineering experience

Strong experience with TypeScript, Node.js, and NestJS

Experience designing scalable backend architectures

Strong understanding of software design principles and maintainable systems

Experience with relational databases (PostgreSQL or similar)

Experience working with Git, CI/CD pipelines, and Docker

Experience mentoring or supporting other engineers

Experience working in agile teams (Scrum or Kanban)

Strong communication skills in English

Nice to Have

Experience with microservices or event-driven architectures

Experience building greenfield or standalone products

Familiarity with AI-related components such as RAG or vector databases

Experience integrating AI services or data-driven systems

Conversational German

What You’ll Own

As a Senior Engineer , you will play a key role in shaping both the technology and engineering culture .

You will:

Design backend systems with clear service boundaries and scalability in mind

Identify technical risks early and propose effective solutions

Contribute to architecture discussions and system design

Improve the team’s engineering standards and productivity

Mentor engineers and contribute to technical decision-making

Deliver high-impact backend features aligned with product and business goals

Why Join Castle Tech?

Build something new – work on a greenfield product from the beginning

Real technical ownership – influence system design and architecture

Modern engineering environment – Node.js, NestJS, and modern tooling

Hybrid work model – office and remote options in Berlin or Munich

Your gear, your choice – MacBook or Windows with the tools you prefer

Growth and development – structured onboarding and coaching

Collaborative team – ambitious engineers who enjoy building great products

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