Senior Backend Engineer (Remote - Poland)

Fresha

Location: Warsaw, Poland — Onsite (4 days on-site) Contract: B2B · 25–40 k PLN net / month + RSUs     The AI-powered OS for beauty, wellness and self-care Fresha is the operating system for the global beauty, wellness and self-care industry, connecting and powering everything from salons and barbers to spas, medspas, fitness studios and health practices. Marketplace + SaaS platform + Fintech   Fresha is the leading AI operating system trusted by millions of consumers and businesses worldwide. Fresha is used by 130,000+ businesses and 450,000+ stylists and professionals worldwide, processing over 1 billion appointments to date. Empowering businesses with an all-in-one platform for bookings, point-of-sale, marketing, and more, while connecting consumers to local services. Your Impact as a Full Stack Engineer   At Fresha, we believe AI is a force multiplier for feature delivery, not just a coding assistant. We provide every engineer with top-tier tooling (Claude, GitHub Copilot, Cursor) to strip away technical toil—so you can focus your energy on shipping high-impact product features. We value engineers who know how to leverage these tools to drive momentum within our 6-week cycles, accelerating the journey from concept to code while maintaining the deep technical judgment to verify, secure, and own the final user experience.    Are you ready to make a significant impact in a fast-paced, autonomous environment? We're seeking an exceptional Backend Engineer to join our cross-functional product team in Warsaw.   What You'll Do:   * Collaborate closely with Product, Design, Frontend, Infrastructure, and Mobile engineers to take features from discovery to rollout and beyond. * Be responsible for features from discovery to observability: technical design, implementation, testing, and rollout. * Design, build, and maintain efficient, scalable, and reliable Ruby/Elixir code. * Work with a polyglot stack (Ruby, Elixir, GraphQL, TypeScript, gRPC) and modern messaging systems (Kafka). * Operate within a Kubernetes-driven environment as we continue moving to a microservice architecture. * Embrace Domain-Driven Design to build high-quality, impactful products from inception to delivery.   To foster a collaborative environment that thrives on face-to-face interactions and teamwork, all Fresha employees work from the office four days per week, with the flexibility to work remotely on Wednesday each week. Warsaw: 20th Floor, Aleje Jerozolimskie 81, 02-001 Warsaw, Poland 

RTB House

Location: Poland (Remote/Flexible) We Are:  RTB House is a global company that provides state-of-the-art marketing technologies for top brands and agencies worldwide. Its proprietary ad-buying engine is the first in the world to be powered entirely by Deep Learning algorithms, enabling advertisers to generate outstanding results and reach their goals at every stage of the funnel.  We are looking for Senior Engineers to support our Bidding Platform organization which is the core of the RTB business, processing over 20 million requests per second to participate in real-time auctions and display advertisements to customers from 90+ countries. If you want to work on technically complex and demanding solutions, this is the opportunity for you! Our Senior Engineers are experts who combine deep technical expertise with a strong sense of ownership, and they take on Tech Lead roles in complex, cross-team projects. You will: * Design and lead implementation of system changes that deliver high performance, scalability and observability for displaying and tracking ads world wide. Develop tools and optimizations to drive measurable improvements in critical user performance metrics. * Implement, test, deploy, monitor and maintain (in all aspects, including setting up environment, writing configuration code, monitor production) HTTP / gRPC services and batch jobs in Java and Python, ensuring adherence to the high engineering standards. * Provide hands-on technical leadership: solving complex system challenges, participating in planning and scoping of projects, and ensuring the implementation of the highest coding standards through participation in code reviews. Requirements: * Excellent understanding of how complex IT systems work - from the hardware level, through software, to algorithms. * Very good knowledge of fundamental Internet protocols and technologies (DNS, HTTP, cookies and others). * Good knowledge of basic methods of creating concurrent programs and distributed systems (from thread level to geo-distributed clusters level). * Practical ability to observe, monitor and analyse the operation of production systems (and draw valuable conclusions from it). * The ability to critically analyze the solutions created in terms of performance (from estimating the theoretical performance of the designed systems to detecting and removing actual performance problems in production). * General knowledge of issues (typical problems and methods of solving them) in the areas of 'high scalability' and 'high availability'. * C1 level in English and Polish. Nice to have: * Experience in the AdTech/Real Time Bidding space. * Experience contributing to Real User Monitoring (RUM) systems. Selected technologies used:  * Java, Python * Aerospike, Memcached * Google Cloud Platform, BigQuery, MinIO * Kafka, Clickhouse * PostgreSQL * Elasticsearch * Kubernetes, Prometheus * Jenkins, Graphite We Offer: * Projects focused on extreme performance and high code quality – clean code and solid code reviews are our standard. * Collaboration within an interdisciplinary, self-sufficient team (including DevOps, database experts, backend developers, product designers, and QA engineers). * Access to modern technologies and the opportunity to apply them in large-scale, high-impact projects. * Cooperation based on B2B contract. * You can cooperate 100 % remotely or choose one of our office spaces in Warsaw or Cracow. Apply now You don't need to tick every box to apply. If you are passionate about software engineering, send us your CV, and we'll review it.

RTB House

Location: Poland (Remote/Flexible) We are:  RTB House is a global company that provides state-of-the-art marketing technologies for top brands and agencies worldwide. Its proprietary ad-buying engine is the first in the world to be powered entirely by Deep Learning algorithms, enabling advertisers to generate outstanding results and reach their goals at every stage of the funnel.  We are looking for engineers to join our Bidding Platform organization which is the core of the RTB business, processing over 20 million requests per second to participate in real-time auctions and display advertisements to customers from 90+ countries. If you want to work on technically complex and demanding solutions, this is the opportunity for you! Our Senior Engineers are experts who combine deep technical expertise with a strong sense of ownership, and they take on Tech Lead roles in complex, cross-team projects.  You will: * Gain deep understanding our ad technology and become familiar with ad industry standards: OpenRTB, MRAID, VAST etc. * Design and lead implementation of high-quality frontend solutions for displaying Ads globally, focusing on performance and scalability. * Write, test, and deploy robust, efficient, and well-documented code in JavaScript/TypeScript, ensuring adherence to the highest coding standards. * Develop monitoring systems to track crucial metrics like reliability or viewability and use data to diagnose and resolve performance bottlenecks. * Collaborate closely with Ads Layouts specialists and backend engineers to ensure smooth data flow and optimal architectural alignment for performance-critical features. * Provide hands-on technical leadership: solving complex system challenges, participating in planning and scoping of projects, and ensuring the implementation of the highest coding standards through participation in code reviews. Requirements: * 8+ years of hands-on experience in developing complex web software * Proficiency in JavaScript/TypeScript and browser APIs. Experience with relevant build tooling (e.g., Webpack, Vite). * Practical experience and strong understanding of Web Performance optimization techniques and advanced loading strategies (caching, asset delivery). * Very good knowledge of fundamental Internet protocols and technologies (DNS, HTTP, cookies and others). * Practical ability to observe, monitor and analyse the operation of production systems (and draw valuable conclusions from it). * Good understanding of full-stack concepts, including system architectures, working with backend APIs and deployment/CI/CD pipelines. * C1 level in English and Polish. Nice to have: * Experience in the AdTech/Real Time Bidding space. * Experience contributing to Real User Monitoring (RUM) systems. We Offer: * Projects focused on extreme performance and high code quality – clean code and solid code reviews are our standard. * Collaboration within an interdisciplinary, self-sufficient team (including DevOps, database experts, backend developers, product designers, and QA engineers). * Access to modern technologies and the opportunity to apply them in large-scale, high-impact projects. * Cooperation based on B2B contract. * You can cooperate 100 % remotely or choose one of our office spaces in Warsaw or Cracow. You don't need to tick every box to apply. If you are passionate about software engineering, send us your CV, and we'll review it.