Role Description 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. Qualifications - 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

• Build teams that push boundaries. • Create startups from the ground up (0→1). • Engage with various products - from AI and FinTech to E-commerce and SaaS. • Collaborate with partners to launch new projects aligning with your skills.

• Develop and maintain our code base in relation to proper technologies (.net core, c#) • Develop and maintain core libraries relating to proper technologies (.net core, c#) • Participate in code reviews and contribute to raising the quality of our product • Research new technologies in accordance to the work • Assist in standardization across the whole company • Ensure applications meet quality standards • Documentation of any work • Collaborate with other teams to define, design, and deploy new features • Troubleshoot and liaise with other departments to solve production issues • Other tasks which may be assigned by the management • Participating in continuing education and training to remain current on best practices, learn new programming languages, and better assist other team members

Role Description DatAds is redefining how marketing and creative teams build winning ads. Our SaaS platform bridges the gap between performance marketers and creative teams by delivering visual ad insights, automated analytics, and AI-powered creative recommendations. The result: faster workflows, smarter decisions, and more high-performing ads – across Meta, TikTok, and YouTube. We’re growing fast, with double-digit month-over-month expansion. Our customers include some of the most innovative eCommerce brands, lead generation companies, and performance marketing agencies across the DACH region – and increasingly, across Europe. Brands like yfood, Greator, Perspective, and Holy trust DatAds to power their creative strategy. If you want to be part of a fast-moving marketing tech startup where your ideas actually shape the product – join us. We're building something big, and we’re just getting started. - Feature Development & Extension across product lines (analytics, inspiration, AI). Possible projects can include: - Build & maintain integrations to ad-platforms like Taboola, Pinterest or Snapchat - Implement AI recommendation system - Extend static AI workflows to dynamic AI agent - Internal Tech Support: Communication with the internal Customer Success team (in English) when bugs or technical questions arise. - End-to-End System Ownership: From system design to deployment, to tech support you'll own entire technology solutions and ensure their operational excellence. We believe in giving maximum freedom – you get the problem, you architect, build and own the complete system solution. Qualifications - Backend: PostgreSQL / SQL - REST APIs - Ideally Node.js + Express.js + TypeScript - Most features involve API updates - Cloud (Azure preferred) - Experience with Docker & serverless containers (Azure Container Apps, Cloud Run) - Event-driven architectures and queue-based background jobs - Frontend: Nuxt.js / Vue.js or Next.js / React - TailwindCSS - Ability to implement clean UI components using modern CSS frameworks - End-to-End Ownership (“Builder Mentality”): Designed, implemented, tested, deployed and maintained features from start to finish. Benefits - Learn from Experience: Work directly with Daniel (CTO), who brings a Master's in Machine Learning and 2 years as Senior Software Engineer in AI infrastructure at HubSpot. You'll have access to mentorship that accelerates your growth. - Ownership & Impact: High responsibility for your projects with a steep learning curve guaranteed. Your code will directly impact how marketing teams worldwide create better ads. - Startup Flexibility: Remote-first culture with flexible working arrangements. Fast communication, flat hierarchies, and a motivated founding team. - Professional Growth: Be part of building something from the ground up. The experience and network you'll build here will be invaluable for your career. - Competitive Compensation: With growth opportunities as we scale. Company Description Mit DatAds haben wir uns ein großes Ziel gesetzt: Wir wollen den Erstellungsprozess von Ad Creatives auf das nächste Level bringen. Unsere Software ist die Brücke zwischen datengetriebenen Performance Marketing und innovativen Creative Teams. Damit ermöglichen wir Performance Marketern und Creative Designern optimal zusammenzuarbeiten und durch tiefere Analysen mehr erfolgreiche Werbeanzeigen zu erstellen. Wir arbeiten mit einigen der größten Marketing Agenturen und starken eCommerce Brands zusammen, wie z.B. Pummys, Beilmann Marketing, Perspective, Health Routine.