A Knowledge Graph and a Tripartite Evaluation Framework Make Retrieval-Augmented Generation Scalable and Transparent

Large Language Models (LLMs) have significantly enhanced conversational Artificial Intelligence(AI) chatbots; however, domain-specific accuracy and the avoidance of factual inconsistencies remain pressing challenges, particularly for large datasets. Designing an effective chatbot with appropriate methods and evaluating its effectiveness is among the challenges in this domain. This study presents a Retrieval Augmented Generation (RAG) chatbot that harnesses a knowledge graph and vector search retrieval to deliver precise, context-rich responses in an exemplary use case from over high-volume engineering project-related emails, thereby minimising the need for document chunking. A central innovation of this work is the introduction of RAG Evaluation (RAG-Eval), a novel chain-of-thought LLM-based tripartite evaluation framework specifically developed to assess RAG applications. This framework operates in parallel with the chatbot, jointly assessing the user's query, the retrieved document, and the generated response, enabling a holistic evaluation across multiple quality metrics like query relevance, factual accuracy, coverage, coherence and fluency. The resulting scoring system is provided directly to users as a confidence score (1 to 100%), enabling quick identification of possible misaligned or incomplete answers. This proposed approach promotes transparency and rapid verification by incorporating metadata email IDs, timestamps into responses. Experimental comparisons against BERTScore and G-EVAL for summarisation evaluation tasks confirm its effectiveness, and empirical analysis also shows RAG-Eval reliably detects factual gaps and query mismatches, thereby fostering trust in high demand, data centric environments. These findings highlight a scalable path for developing accurate, user-verifiable chatbots that bridge the gap between high-level conversational fluency and factual accuracy.