The Model Context Protocol (MCP) is an open standard that lets AI agents call external tools through a uniform interface. An MCP memory server is one such tool provider: instead of returning weather or search results, it stores and retrieves durable context — decisions, files, past sessions — so the agent can remember across conversations.
Most agents have no long-term memory: Claude Code, Codex and Cursor each write history to their own files and never read the others'. An MCP memory server sits beside them and answers questions like “what did we decide about auth in this repo?” or “resume where the last session stopped” — for any client that speaks MCP, from one shared store.