Castle Tech GmbH – Berlin or Munich (Hybrid)
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 in shaping 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 OnBuild 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 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
Exploring modern AI-driven development workflows
This role is for engineers who see AI as a tool to enhance engineering, not replace good engineering practices.
Your SkillsMust Have5+ 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
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
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
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
AI-forward engineering culture
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
