Senior Full Stack Engineer (B2B - Warsaw)

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. Role Overview   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.    Given our exciting and progressive growth plans, we are looking for an exceptional Senior Backend Engineer to come join our global business.   Reporting directly to the Team Lead, and working collaboratively in a cross-functional product team within a tribe, you will be accountable for designing and developing applications and coordinating with the rest of the team working on different layers of the infrastructure Fresha.   This is a great opportunity for someone looking to work in a fast-paced and changing environment, who likes to work autonomously, enjoys a challenge and wants to make an impact!   To foster a collaborative environment that thrives on face-to-face interactions and teamwork, you will need to travel for one week once a quarter to our quarterly team events (in London/Warsaw/Prishtina).

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.

RTB House

We are:  RTB House is a global company that provides state-of-the-art marketing technologies for top brands and agencies worldwide. Our proprietary ad-buying engine is the first in the world to be powered entirely by Deep Learning algorithms, enabling advertisers to achieve outstanding results and meet their goals at every stage of the funnel. Join RTB House and lead our AI Engineering Lab, a team dedicated to pioneering innovation and boosting engineering productivity by leveraging the latest advancements in Agentic AI. We are looking for a hands-on technical leader with a strong, traditional software engineering background. In this role, you won't just be writing custom code from scratch. You will be an architect of efficiency. Our approach is highly pragmatic: we build internal tools and autonomous agents to supercharge our engineering workflows. You will be expected to navigate the "build vs. buy/integrate" landscape, determining when to leverage off-the-shelf LLM products and when to architect a custom, high-performance solution. You will: * Drive Technical Excellence: Act as a technical pillar within the Lab, implementing high-standard code and sophisticated system designs. You will mentor mid-level peers and lead deep-dive code reviews. * Architect Multi-Agent Systems: Design and deploy distributed systems and multi-agent architectures that automate complex engineering tasks. You will own the architectural decisions for "build vs. integrate" strategies. * Innovate with Agentic AI: Spearhead the evaluation and prototyping of LLMs, Agentic frameworks, and Model Context Protocols (MCPs). You will transform theoretical AI advancements into production-ready tools. * Own the Full Lifecycle: Take responsibility for the entire development cycle. From initial concept and API integration to production deployment and long-term scalability. * Influence Product Strategy: Partner with Product and Engineering Managers to ensure the Lab’s innovations align with the broader company roadmap and provide measurable ROI to our developers. Desired experience: * Pragmatic Architect: Proven ability to evaluate third-party tools and vendor solutions against custom-built software to find the most efficient path forward. * Technical Stack: High proficiency in Python is mandatory. Significant experience with at least one other language (Java, Go, TypeScript, or Scala) is highly preferred. * AI/ML Implementation: Hands-on experience integrating LLMs into production environments. * Systems Thinker: Ability to define technical roadmaps for specific features and drive high-level design choices that prioritize maintainability and performance. * C1 level in English and Polish. Nice to have: * Direct experience building internal developer tools, custom Model Context Protocols (MCPs), or using Agentic AI frameworks (e.g., Vercel AI SDK, LangChain, AutoGen, Agent Development Kit). * Experience with cloud platforms (AWS, GCP, Azure) and containerization technologies (Docker, Kubernetes). * Familiarity with the ad-tech industry and real-time bidding (RTB) 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.