Euclid-MCP Ships an MCP Server for Prolog, Arguing Semantic RAG Is Fundamentally Unsuited to Rule Enforcement

arXiv 2607.21412·medium signal

Bartolomeo Bogliolo released an open-source Model Context Protocol server that delegates multi-step logical reasoning to SWI-Prolog, introducing Euclid-IR — an engine-agnostic Horn-clause intermediate representation designed to be easy for LLMs to emit and straightforward to compile to Prolog or other backends. The tool interface supports a translate-run-inspect-repair loop so the calling LLM retains full access to proof traces and derivation logs rather than an opaque answer. Evaluated on an IT security and compliance use case, LLMs alone sufficed on small knowledge bases but hallucinated systematically as the base grew, while Euclid-MCP returned exact answers with lower latency and more compact outputs.