Senior Data Annotator Jobs in Madrid

About The Role Senior data annotator jobs in Madrid at Rex.zone focus on high-precision data labeling and evaluation workflows that improve large language model (LLM) training pipelines. This is a remote, full-time role emphasizing training data quality, auditability, and consistent guideline-driven execution. What You Will Do Deliver high-accuracy data labeling across NLP tasks (e.g., named entity recognition, classification, ranking) and computer vision annotation when neededRun QA evaluation, peer review, and adjudication to resolve disagreements and improve inter-annotator agreementEnforce annotation guidelines compliance; document edge cases and propose guideline refinementsExecute QA sampling plans, error analysis, and root-cause reporting to improve training data qualitySupport RLHF and prompt evaluation by ranking responses, writing preference rationales, and validating reward-model training setsCollaborate with project leads and stakeholders to track throughput, accuracy, rework rate, and audit pass rates Required Qualifications Mid-Senior experience in data annotation, data labeling, or QA evaluation for ML datasetsStrong command of annotation guidelines compliance and consistent decision-making in ambiguous casesFamiliarity with LLM training pipelines, large language model evaluation, prompt evaluation, and RLHF workflowsComfort working in a remote, metrics-driven delivery environment Quality Standards Maintain targets for accuracy, inter-annotator agreement, audit pass rates, and low rework ratesSupport traceable and reproducible pipelines through gold set verification and documented decision logs Apply Apply through Rex.zone and highlight your data labeling depth, QA evaluation rigor, and experience improving training data quality for LLM training pipelines.