MCP vs RAG

Definition

MCP and RAG address different aspects of how context is provided to a language model: Model Context Protocol (MCP) governs how all contextual inputs are structured and controlled, while Retrieval-Augmented Generation (RAG) focuses specifically on retrieving external information to include in that context.

Purpose

The purpose of comparing MCP and RAG is to clarify their distinct roles in modern AI systems and to help system designers choose the appropriate mechanisms for context management, retrieval, and control.

Key Characteristics

• MCP defines rules for assembling and governing the entire model context, while RAG supplies retrieved content as one possible input to that context
• MCP emphasizes determinism, policy enforcement, and auditability, whereas RAG emphasizes relevance and coverage of external information
• RAG operates as a retrieval-and-injection mechanism, while MCP operates as a higher-level orchestration layer
• RAG can exist without MCP, but MCP commonly incorporates RAG as a component
• MCP addresses context structure and control, while RAG addresses data access

Usage in Practice

In practice, MCP and RAG are used together in enterprise and agentic systems, where RAG retrieves relevant data and MCP determines how that data is prioritized, constrained, and combined with instructions, tools, and memory within the context window.

Related Terms