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

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

Freelance Contract | 9–12 months
Remote from Brazil

About the Project

Castle Tech GmbH is building a new standalone product from the ground up and is looking for an experienced Senior Backend Engineer (Node.js / NestJS) to join us on a freelance basis for 9–12 months.

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 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

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 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 (written and verbal)

Availability for 9–12 months, starting as soon as possible

Comfortable working remotely with European time zone overlap (able to attend meetings during CET/CEST business hours)

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

Previous experience working with European clients or distributed teams

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

Contract Details

Duration: 9–12 months (with potential for extension)

Location: Remote from Brazil

Start date: ASAP

Engagement type: Freelance / Contract (B2B or international contractor agreement)

Work arrangement: Fully remote with expected overlap during European business hours (CET/CEST)

Time zone: Flexible, with core collaboration hours aligned to Central European Time

Why Work With Castle Tech?

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

Real technical ownership – influence architecture and system design

Modern engineering environment – use the latest tools and workflows, including AI-assisted development

Collaborative team – work with experienced engineers, product managers, and designers

Remote-first mindset – async-friendly culture with clear communication practices

International exposure – work with a European tech company from Brazil