About The RoleWhat if the code you write could directly power the AI systems shaping how millions of people interact with technology? We're looking for Back End Developers in Madrid to design, build, and optimize the server-side systems and APIs that drive cutting-edge AI products — from data pipelines and model-serving infrastructure to scalable microservices that handle real-world traffic at scale.This is a fully remote, flexible contract role. Whether you're a seasoned engineer looking for meaningful project work or a strong developer ready to apply your skills to AI-adjacent infrastructure, this is your chance to build things that matter.Organization: AlignerrType: Hourly ContractLocation: RemoteCommitment: 10–40 hours/weekWhat You'll DoDesign, develop, and maintain robust back end services, APIs, and data pipelinesBuild scalable, high-performance server-side architecture to support AI training and inference workloadsWrite clean, well-documented, and testable code following engineering best practicesIntegrate with databases, message queues, cloud services, and third-party APIsOptimize system performance, reliability, and scalability as usage growsCollaborate asynchronously with distributed teams of engineers, researchers, and product leadsTroubleshoot production issues, conduct code reviews, and contribute to architectural decisionsWork independently on task-based and project-based assignments on your own scheduleWho You AreProficient in one or more back end languages — Python, Go, Java, Node.js, Rust, or similarSolid understanding of RESTful API design, microservices architecture, and distributed systemsExperienced with relational and/or NoSQL databases (PostgreSQL, MongoDB, Redis, etc.)Comfortable working with cloud platforms such as AWS, GCP, or AzureFamiliar with version control (Git), CI/CD pipelines, and containerization (Docker, Kubernetes)Strong problem-solving skills and the ability to debug complex systems independentlySelf-motivated, reliable, and effective when working asynchronously without close supervisionClear communicator who can document decisions and collaborate across time zonesNice to HaveExperience building infrastructure for machine learning or AI systemsFamiliarity with data processing frameworks (Apache Kafka, Spark, Airflow, or similar)Background in performance optimization, caching strategies, or high-throughput systemsKnowledge of authentication, authorization, and security best practicesExperience with serverless architectures or event-driven design patternsContributions to open-source projects or a strong portfolio of personal/professional workWhy Join UsWork on cutting-edge AI infrastructure projects alongside leading research labsFully remote and flexible — set your own hours and work from anywhereFreelance autonomy with access to meaningful, technically challenging workBuild systems at the intersection of software engineering and artificial intelligenceCollaborate with a global network of talented engineers and researchersPotential for ongoing work and contract extension as new projects launch
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