--- title: "What is the Model Context Protocol?" canonical: "https://xerj.org/science/model-context-protocol" updated: "2026-11-14" source: "content/science/model-context-protocol.md" --- # What is the Model Context Protocol? **Short answer** (updated 2026-11-14): What is the Model Context Protocol? It is an open protocol that lets a host, such as Claude Code or Cursor, call tools on a local or remote node. XERJ exposes search, definition lookup, and memory tools over MCP. 24 tools are listed on main, 21 of them with no Corpus Hub key. **Key number:** 24 tools are listed on main, 21 of them with no Corpus Hub key. (as of 2026-10-19; source: [/answers/local-code-search-mcp-fewer-tokens-than-grep](/answers/local-code-search-mcp-fewer-tokens-than-grep)) **TL;DR** The Model Context Protocol, or MCP, is an open protocol that lets a host such as Claude Code or Cursor call tools on a local or remote node. XERJ exposes search and memory as those tools. ## Agent prompt ```text Act as a coding agent. Read https://xerj.org/llms.txt, install XERJ, start a local node, index one folder I point you to, and run one search so I can see a cited passage. ``` *Figure: MCP is the open protocol documented at modelcontextprotocol.io. The 24-tool / 21-without-hub-key count is the published figure from the local code-search MCP answer (inspector listing on main, 2026-10-19).* ## How it works A host starts an MCP client. The client connects to a node that speaks the protocol and advertises a list of tools. When the model needs one of those tools, it issues a tool call. The node runs the tool and returns the result to the host. The protocol is the contract. It does not itself index your files or store your facts. ## How XERJ uses it `xerj mcp` exposes tools such as search, definition lookup, and memory tools. The model can retrieve a cited passage or a stored fact instead of reading a whole tree. 24 tools are listed on main, 21 of them with no Corpus Hub key. That count is from the inspector listing on 2026-10-19, published on the [local code-search MCP answer](/answers/local-code-search-mcp-fewer-tokens-than-grep). Memory tools are explained under [agentic memory](/science/agentic-memory). A how-to for memory over MCP is [what is an MCP memory server](/answers/what-is-an-mcp-memory-server). ## History and research MCP is documented at the official site, [modelcontextprotocol.io](https://modelcontextprotocol.io). This page uses that site as the protocol reference, and XERJ's published tool count as the product figure. It does not invent a paper for the protocol. ## Guides Guides: [code search MCP for Claude Code](/answers/code-search-mcp-for-claude-code), [local search MCP for Codex and Cursor](/answers/local-search-mcp-for-codex-and-cursor) and [MCP code search compared](/compare/best-mcp-server-local-code-search-2026). ## Related terms [Agentic memory](/science/agentic-memory) and [syntax-aware search](/science/syntax-aware-search). ## FAQ ### What is MCP? The Model Context Protocol is an open protocol for hosts to call tools on a node. The official documentation is at modelcontextprotocol.io. ### How does an agent reach XERJ over MCP? The host starts a client, the client connects to xerj mcp, and the model issues a tool call for search, definition lookup, or memory. ### How many tools does XERJ expose? 24 tools are listed on main, 21 of them with no Corpus Hub key. That count is from the inspector listing on 2026-10-19, published on the local code-search MCP answer. ### Is MCP a XERJ protocol? No. MCP is an open protocol. XERJ is one node that speaks it, so an agent can search and store memory without reading a whole tree. ## Evidence - 24 tools are listed on main, 21 of them with no Corpus Hub key. — [/answers/local-code-search-mcp-fewer-tokens-than-grep](/answers/local-code-search-mcp-fewer-tokens-than-grep) ## Related - [Local code search MCP that uses fewer tokens than grep](/answers/local-code-search-mcp-fewer-tokens-than-grep) - [What is an MCP memory server?](/answers/what-is-an-mcp-memory-server) - [What is agentic memory?](/science/agentic-memory) - [What is syntax-aware search?](/science/syntax-aware-search) - [What is context engineering?](/science/context-engineering) (same intent: Science) - [BM25 vs vector search](/science/bm25) (same intent: Science) - [What is Corpus Hub?](/science/corpus-hub) (same intent: Science)