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Design and Evaluation of a Retrieval-Augmented Generation System for Czech

Anna Sajdoková

Digital Repository (National Repository of Grey Literature), 2026

Abstract

The goal of this thesis is to design, implement, and evaluate a Retrieval-Augmented Generation (RAG) pipeline for Czech. We systematically analyze individual RAG compo- nents, including PDF preprocessing, text chunking, and both embedding and generative models. We evaluate a BM25 baseline and eleven embedding models using two Czech datasets: DaReCzech-Test and a custom-made Wikipedia-NLP. Additionally, we compare multiple generative models within an end-to-end RAG pipeline in a small-scale study with six participants. In retrieval, Qwen3-embedding:4B achieves the best performance. BM25 remains a strong CPU-only baseline outperforming smaller embedding models. For gen- eration, Llama 3.3 is preferred by users, whereas GPT-OSS achieves the highest factual accuracy. We release a pre-packaged Docker container based on OpenWebUI with our best-performing RAG configuration.

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