Freelance Backend Developer

Flying Bisons is a premier Digital Consulting and Delivery company situated in the vibrant city of Warsaw, Poland. Our mission is to empower our clients to Unleash Digital Potential™. We excel in discovering, defining, designing, and developing top-tier digital products that yield impactful business results for our clients, creating outstanding digital experiences for millions worldwide.What sets us apart is our comprehensive end-to-end process that equips us to tackle every challenge with the assurance of achieving optimal results. Our areas of expertise encompass Research, Digital Strategy, Branding, Content Creation (Written, Photos, Videos), Product Design, Web & Mobile Development, Data Analytics, and AI.Become part of our dynamic team of 120 professionals and collaborate in crafting groundbreaking products and exhilarating experiences for notable brands(such as Mercedes AMG, IKEA, KFC, eObuwie, Żabka, Sanofi, Zain) and innovative startups (like Booksy, Nethone, Telemedi, or DevSkiller)!We are in the process of building a curated network of talented freelance Backend Developers to engage for both current and future projects. When you apply to join our freelancer base, your application will be assessed and kept on file. You may not be contacted immediately, but once a project aligns with your expertise, you will receive an invitation to participate, allowing you to accept or decline based on your availability. If you're interested in joining our talent pool, please submit your CV. We will reach out as soon as a fitting opportunity becomes available.Are you a self-motivated and reliable professional? If so, we are eager to hear from you!

Join Netguru, a pioneering force in digital commerce, as we assist renowned brands in modernizing their B2B solutions, marketplaces, and retail ecosystems. Since our inception in 2008, we have empowered businesses through innovative technology, AI-driven personalization, and exceptional engineering and design teams. As a certified B Corporation®, we proudly serve major brands such as IKEA, VW, OLX, Delivery Hero, Żabka, Wolt, Careem, and Vinted.We are currently seeking a Senior Backend Engineer with robust architectural expertise to engage in a long-term project for a European client in the laboratory and biotech sector. This position is a single-developer project, requiring close collaboration with the client’s internal teams and laboratory stakeholders to clarify requirements, outline the project scope, and enhance existing backend processes. Strong communication skills are vital, as you will frequently participate in technical discussions with LIMS and laboratory teams. Your role will encompass hands-on development, legacy code refactoring, and contributing to a scalable, well-structured backend architecture. Please note that candidates must be based in the EU due to client stipulations.Position: Senior Backend Engineer (Java / Architecture)Contract: Freelance / B2B – Remote (EU Only)Rate: 36–50 EUR/hourLanguage: English C1Key ResponsibilitiesOperate independently as the sole backend engineer on the project.Refactor and modernize legacy backend systems.Enhance and expand existing microservices and backend integrations.Maintain and develop REST and SOAP interfaces.Engage with laboratory teams and LIMS stakeholders to define requirements.Guarantee stable operation of backend services in an on-premise Kubernetes environment.Work collaboratively with internal client teams to ensure architectural consistency.QualificationsTechnical Skills & ExperienceExtensive experience with Java (Spring / Spring Boot).Strong architectural and problem-solving abilities.Proficient in designing and maintaining REST APIs.Familiarity with SOAP services.Experience in microservices environments.Hands-on experience with Kubernetes (preferably on-premise setups).Background in working with or integrating LIMS systems.Solid understanding of refactoring and modernizing legacy code.Excellent communication skills for direct collaboration with laboratory stakeholders.Proficiency in English at C1 level.Must be based in the European Union.BenefitsIn return, we offer:100% remote, flexible work environment;Access to cutting-edge technology and tools;Opportunities for professional development.

Join our dynamic team at Lingarogroup as a Backend Developer! In this role, you will be responsible for designing, implementing, and maintaining server-side applications and databases, ensuring high performance and responsiveness to requests from the front-end. You will work closely with front-end developers to integrate user-facing elements with server-side logic.We are looking for someone who possesses a strong understanding of backend technologies, is highly motivated, and thrives in a collaborative environment.

Role overview Talan is seeking a Mid-Level Backend Spark Developer to join the team in Warsaw. This role centers on building and maintaining backend systems, with Apache Spark as a primary tool. The work directly supports ongoing projects and plays a key part in meeting team objectives. What you will do Develop backend solutions that use Spark as a central technology Collaborate with colleagues from various disciplines to deliver dependable software Support project progress by helping meet milestones and upholding technical standards Location This position is based in Warsaw.

Join Larian Studios as a Backend Developer, where you'll play a pivotal role in creating immersive gaming experiences. We are looking for innovative thinkers passionate about backend technologies to help design and implement scalable systems that enhance our gaming platforms.

Join our dynamic team at Renmoney as a Java Backend Developer, where you will contribute to our core engineering teams, including Banking, Loans, Core Tech Platform, and Cards. Our teams are focused on developing high-impact, backend-heavy systems that drive essential financial products and internal platforms.At Renmoney, we prioritize engineering excellence—not only in delivery speed but also in system quality and the artistry of software development. We are cultivating a collaborative engineering culture that values clear communication, thoughtful architecture, rigorous testing, and teamwork.Our tech stack includes: Java • Spring Boot • AWS (EKS) • MySQL • Kafka • Redis • Grafana • Prometheus.

Join our dynamic team at Evolution as a Backend Developer specializing in Scala. In this role, you will be responsible for designing, implementing, and maintaining high-performance backend systems that are scalable and robust. You will collaborate with cross-functional teams to deliver innovative solutions that meet our clients' needs.

Jobgether is hiring a Senior Node.js Backend Developer in Poland for a partner company. This role joins an experienced engineering team focused on building secure, scalable backend systems that power digital financial services worldwide. Key Responsibilities Design and develop backend solutions with Node.js for global financial products Build and maintain mission-critical services and APIs supporting real-time transactions Architect infrastructure for distributed systems to ensure reliability Optimize backend performance while maintaining strong security standards Collaborate with engineers across different regions Contribute to advancing next-generation financial technology Requirements Proven experience in backend architecture and distributed systems Advanced skills in Node.js development Ability to tackle complex technical challenges Interest in scaling secure, real-time applications Self-motivated and comfortable working with autonomy in a remote-first environment Located in Poland Work Environment This is a remote-first position. The team emphasizes independence, responsibility, and continuous learning. Senior Node.js Backend Developers here work closely with talented colleagues and play a direct role in shaping products used by customers around the world.

Dołącz do naszego zespołu jako Senior Backend Developer! Szukamy utalentowanej osoby, która będzie odpowiedzialna za długofalowe rozwijanie i utrzymywanie aplikacji backendowych. Twoje zadania będą obejmować optymalizację istniejących rozwiązań oraz zapewnienie zgodności z najlepszymi praktykami wytwarzania oprogramowania. Jeśli jesteś pasjonatem technologii i chcesz pracować w dynamicznym środowisku, to ta oferta jest dla Ciebie!

Join Netguru, a leader in the digital commerce landscape, as we partner with renowned brands to elevate their B2B solutions, marketplaces, and retail ecosystems. Since our inception in 2008, we have empowered businesses with state-of-the-art technology, AI-driven personalization, and top-notch engineering and design teams. As a certified B Corporation®, we take pride in our collaborations with major brands such as IKEA, VW, OLX, Delivery Hero, Żabka, Wolt, Careem, and Vinted.How does freelancing work at Netguru?As a freelancer at Netguru, you have the flexibility to choose your working hours, location, and project tasks. We align your skills with suitable projects, providing you access to diverse opportunities across various industries. This not only enhances your experience but also allows you to broaden your skill set.Moreover, Netguru freelancers can engage in full-time collaborations, truly becoming integral members of our team. Are you ready to make a significant impact? Join us, and let’s create stunning software together.Currently, we are seeking a Senior Frontend Developer to join our team.

Highlights Location: Fully Remote (CET hours preferred) Compensation: €5,100 - €6,300 per month + stock options Language: Russian-speaking team About Fundraise Up At Fundraise Up, we are revolutionizing the way nonprofits receive donations. Our innovative platform facilitates a fast, seamless, and user-friendly donation experience, empowering organizations to harness the power of generosity. Our technology processes tens of millions of dollars in donations monthly, focusing on enhancements that lead to faster load times, higher conversion rates, and accessible design. Trusted by renowned nonprofits like UNICEF and the Alzheimer’s Association, and with a stellar 4.9/5 rating on leading software review platforms, our product is recognized for both its effectiveness and quality. A Truly Global Product We serve nonprofit organizations across North America, the UK, Australia, and Europe in the enterprise sector. Our robust product ecosystem includes a modern checkout experience, customizable widgets, donor and organization portals, admin tools, and multiple internal applications. Our backend technology stack features Node.js (Koa, NestJS) and MongoDB. The frontend utilizes Webpack, Vue.js, and React, with a significant portion of the codebase written in TypeScript. For high-volume messaging and background processing, we implement Kafka and Bull (Redis). Analytics are managed through ClickHouse, while Elasticsearch is utilized for search functionalities. The Team We are a diverse team of over 160 professionals, including more than 80 engineers, distributed across Spain, Poland, Portugal, Georgia, Armenia, Serbia, Turkey, and Cyprus. Our team members typically possess 5-10+ years of experience, fostering a culture of technical curiosity and knowledge sharing. Despite our size, we maintain a close-knit team environment where every contribution is valued, and collaboration is key. We prioritize strong engineering practices and a product-first mindset, hosting biweekly engineering forums to share insights and celebrate achievements. Join a team where quality, mentorship, and mutual respect are at the forefront. About the Role As a Backend Developer, you will be instrumental in architecting the core engine that drives our global platform. You will tackle complex challenges within a high-load, distributed system, constructing and scaling the infrastructure that processes millions in donations. This role goes beyond maintenance; it involves active development and innovation.

Join our dynamic team at dev2 as a Lead Software Engineer specializing in backend development. You will play a pivotal role in designing and implementing robust, scalable, and high-performance software solutions. Your expertise will drive innovation and help shape the future of our products while mentoring junior engineers and collaborating with cross-functional teams.

Location: Poland About Us: RTB House stands at the forefront of marketing technology, delivering cutting-edge solutions to leading brands and agencies around the globe. Our proprietary ad-buying engine is the world's first to utilize Deep Learning algorithms exclusively, empowering advertisers to achieve remarkable results at every stage of their marketing funnel. We are on the lookout for a Backend Python Developer to become an integral part of our internal team at RTB House. In this role, you will engage in the development of applications and tools that directly enhance our real-time bidding operations. Collaborating with seasoned engineers and product teams, this position offers a fantastic opportunity for developers eager to expand their skill set, tackle real-world challenges, and create robust software that makes a tangible impact.

Join Netguru, a leading partner in digital commerce, as we empower top brands to innovate their B2B solutions, marketplaces, and retail ecosystems. Since our inception in 2008, we have been at the forefront of technology, utilizing AI-powered personalization and delivering exceptional engineering and design services. As a certified B Corporation®, we are proud to partner with industry giants such as IKEA, VW, OLX, Delivery Hero, Żabka, Wolt, Careem, and Vinted.What does freelancing look like at Netguru?As a Netguru freelancer, you have the flexibility to define your work style. Choose your working hours, location, and project types that align with your expertise.We ensure that you are paired with projects that match your skills, offering diverse opportunities across various industries. This approach not only enhances your experience but also allows for skill diversification.Moreover, our freelancers can engage in full-time collaborations, becoming integral members of our teams.If you are ready to make a significant impact, join Netguru, and let’s create remarkable software together.We are currently seeking AI-savvy Mid and Junior Python Developers to contribute to our client’s projects.Details:Freelance assignmentFull-time commitmentB2B contractStart date: ASAPDuration: 8-12 months (with a possibility of extension)Working hours: 9 AM - 5 PM CETSalary for Junior: up to 24 EUR/hourSalary for Mid: up to 34 EUR/hourYou will have the opportunity to work on one of three impactful projects for our client:Project #1: Develop a universal health profile for users and their families, transforming fragmented records into insightful products that promote longer, healthier lives.Project #2: Address the doctor capacity crisis by enhancing doctors' ability to manage 30% more patients without compromising quality or risking burnout.Project #3: Create a marketplace that serves as the primary access point for healthcare services across various channels.

MasterBorn is seeking a Junior Backend Developer with a focus on Node.js. This position is open to candidates based in Wrocław or those who prefer to work remotely. Role overview This role centers on developing server-side applications using Node.js. Junior Backend Developers at MasterBorn collaborate with experienced colleagues and contribute to a range of technical projects. The position offers a chance to build practical skills and gain exposure to modern backend technologies. What you will do Work on backend features and APIs using Node.js Collaborate with other developers to deliver project goals Contribute to the development and maintenance of server-side applications Requirements Interest in backend development and Node.js Willingness to learn and grow as part of a team Ability to work from Wrocław or remotely

Join Netguru, a reputable leader in digital commerce, as we partner with prominent brands to revolutionize B2B solutions, marketplaces, and retail ecosystems. Since our inception in 2008, we have empowered businesses with innovative technology, AI-driven personalization, and exceptional engineering and design expertise. Proudly certified as a B Corporation®, we are trusted by industry giants including IKEA, VW, OLX, Delivery Hero, Żabka, Wolt, Careem, and Vinted.Freelancing at Netguru:As a Netguru freelancer, you have the unique opportunity to tailor your work environment. You will determine when, where, and how you engage with projects and tasks. Our team ensures that your assignments align with your skills and interests, providing you with diverse opportunities across various industries to enhance your experience and skill set.Moreover, as a Netguru freelancer, you are not just an outsider; you become an integral part of our team with the possibility of full-time collaboration.Are you ready to make a significant impact? Come aboard Netguru, and let’s create exceptional software together.We are currently looking for a skilled Senior Golang Developer.This role is a freelance position on a B2B contract, focusing on the development and scaling of distributed systems and services. The position is 100% remote and requires the selected candidate to be available to start as soon as possible.B2B Contract | Up to 39 EUR/h | Remote | Immediate Start

Join HelloFresh as a Senior Backend Engineer specializing in Deliveries & Orders, where you will design and develop robust backend systems that drive our logistics and order management processes. You will collaborate with cross-functional teams to enhance our platform, ensuring a seamless experience for our customers.

About Our Team At SumUp, we provide a comprehensive Point-of-Sale (POS) solution designed to empower businesses such as cafes, shops, bars, and salons to streamline operations and foster growth. Our platform encompasses a variety of features including product catalogs, inventory management, business analytics, compliance assistance, and loyalty programs. The Fiscalization team is dedicated to ensuring compliance in countries like Italy, Sweden, Norway, Belgium, and Austria, among others. We are also pioneering the integration with third-party services for fiscalizing receipts. As a Senior Backend Engineer, you will work alongside a vibrant, cross-functional team comprising Product Managers, Designers, Engineering Managers, and fellow engineers. Your Role In this position, you will develop secure backend systems that ensure SumUp's POS products are compliant across various countries on our roadmap. You will collaborate with the Fiscalization squad to devise unique solutions tailored to the challenges in each market. We are looking for a developer who values user-centric design, precision, and seamless collaboration. You will excel in a structured communication environment and thrive in a cross-functional team. This is a B2B role based in Warsaw. Key Responsibilities Design and maintain fiscal compliance solutions to support SumUp's expansion across Italy, Sweden, Norway, Belgium, Austria, and other European markets. Develop integrations with third-party services for receipt fiscalization and regulatory reporting. Navigate SumUp's intricate POS ecosystem and familiarize yourself with fiscalization frameworks across multiple jurisdictions. Work collaboratively with team members and stakeholders distributed across 5+ cities in a hybrid working model. You Will Succeed in This Role If You Have: 5+ years of experience in backend engineering with expertise in Java and/or Kotlin. A solid understanding of system architecture, design principles, data modeling, and API development. Hands-on experience with distributed and fault-tolerant systems. Proficiency in AWS and Kubernetes. Strong knowledge of Kafka, PostgreSQL, and CQRS.

Join Valtech, a leading experience innovation company and trusted partner to some of the world's most recognized brands. We offer our team members numerous growth opportunities, a values-driven culture, and the chance to shape the future of customer experiences.The OpportunityAs a Senior Salesforce Marketing Cloud Developer at Valtech, you will engage in an environment focused on continuous learning, impactful contributions, and professional advancement. Your role will involve pioneering new digital solutions and reimagining customer experiences, ultimately driving transformation across various industries.

Flying Bisons is a premier Digital Consulting and Delivery firm located in the vibrant city of Warsaw, Poland. Our mission is to empower our clients to Unleash Digital Potential™. We specialize in discovering, defining, designing, and developing top-tier digital products that yield significant business outcomes, crafting digital experiences for millions globally.What sets us apart is our comprehensive end-to-end process, enabling us to tackle every challenge with the assurance that we deliver exceptional results. Our expertise spans Research, Digital Strategy, Branding, Content Creation (including Written, Photography, and Video), Product Design, Web and Mobile Development, Data Analytics, and Artificial Intelligence.Become a part of our dynamic team of 120 professionals as we co-create industry-defining products and exhilarating experiences for renowned brands(Mercedes AMG, IKEA, KFC, eObuwie, Żabka, Sanofi, Zain) and innovative startups(such as Booksy, Nethone, Telemedi, and DevSkiller).We are assembling a curated network of skilled freelance React Native Developers to collaborate on current and forthcoming projects. By applying to join our freelancer pool, you will undergo an evaluation process and remain in our records for future opportunities. While you may not be contacted immediately, when a project aligned with your expertise arises, you will be invited to participate, with the option to accept or decline based on your availability. If you are enthusiastic about joining our talented pool, please submit your CV. We will reach out once a fitting opportunity emerges.Are you a self-motivated and reliable professional? If so, we eagerly await your response!Contract type: B2B