Senior Backend Engineer (Node.js)

We are the company behind CKEditor — an open-source rich text editor used by millions of people around the world. We are part of Tiugo Technologies, a family of API-first developer platforms (CKEditor, TinyMCE, ButterCMS, Uploadcare) focused on content creation and digital collaboration.Your role:As an Engineer on our AI team, you will drive the evolution of AI capabilities powering CKEditor 5 — working at the intersection of AI and content creation, where LLMs meet their most natural application: text processing. You'll design prompt strategies, integrate models from providers like OpenAI, Anthropic, and Google Gemini, and build intelligent features such as contextual text predictions, automated content generation, and advanced text processing. Check out what we've built so far at https://ckeditor.com/ckeditor-5/demo/ai and imagine where you could take it next.Our core stack is TypeScript and Node.js. We're looking for an engineer with genuine passion for AI and a solid backend foundation — someone who can build production-grade services, not just prototypes, and who balances cutting-edge innovation with robust implementation.Key Responsibilities:Design, build, and maintain backend services for CKEditor 5 - including REST APIs, real-time streaming, event-driven processing, and data persistence.Build and maintain a multi-service architecture with message queues, caching, and async communication patterns.Engage in code reviews, pair programming, and cross-functional collaboration to ensure the highest quality results.Write clean, maintainable, and well-structured code, balancing readability with appropriate documentation.Share best practices on programming standards, tools, and processes to foster continuous improvement.To be successful in this role you need the following:Over 5 years of software development experience.Strong proficiency in TypeScript and Node.js.Experience building and maintaining backend services - REST APIs, relational databases (PostgreSQL), message queues, Docker.Fluency in Polish (minimum C1) and good command of English (minimum B2)Excellent problem-solving skills and the ability to think critically and creatively.Outstanding communication skills, both verbal and written.Nice to have:Experience integrating third-party APIs (LLM providers, external services).Understanding of AI/LLM concepts - prompt engineering, function/tool calling, streaming.Experience with cloud infrastructure (AWS - SQS/SNS, S3, ECR).Familiarity with observability tools (OpenTelemetry, tracing)Curiosity about AI and willingness to learn how LLMs work.Experience with event-driven architectures and real-time data processing (streaming, WebSockets, or similar).Why join CKSource:Our people are a huge part of what makes CKSource a great place to work! Aside from a great team, some of our benefits include:B2B contract-based monthly remuneration is 27.000 - 32.000 PLN + VAT or its equivalent on the employment contract.Quarterly and annual financial bonuses depending on the company’s performance.Flexible schedule and the possibility to work fully remotely.Professional development resources (up to 5 days of additional leave and 6 000 PLN yearly).LinkedIn Learning access.Extra leave for Tiugo Day - our company’s foundation day and your birthday.English lessons with a native speaker and an online language platform where you can learn English, Spanish, and German.Access to a mental health and well-being platform with 24/7 dedicated psychological support.Private medical care (Enel Med or Medicover) and Multisport card.2 weeks of paid parental leave for our contractors.Recruitment processHR interview.Technical interview with Jacek Bogdański (Engineering Manager).Interview with Bartek Czerwonka (Senior Director of Engineering).