# Chapter 10 - The Nervous System (MCP and Protocol Interop) | Loop Engineering

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# Chapter 10 - The Nervous System: MCP and Protocol Interop

                Last updated 2026-07-13. Review the protocol-side primary sources behind Chapter 10 and explore the [live MCP server catalog](/mcp/) for current implementations.

### Companion activity

Use the [MCP catalog](/mcp/) to evaluate one server by asking what it exposes, who authorizes it, what gets logged, and what judgment still lives outside the protocol.

### What this chapter argues

                MCP - the Model Context Protocol - is one exchange layer through which AI applications can discover and invoke tools or access context. It does not create judgment, governance, security, or learning on its own. The nervous-system analogy is useful but limited: hosts and implementations still decide what is exposed, authorized, logged, reviewed, and retained. A defensible decision record therefore depends on explicit logging and decision context around tool use, not on protocol traffic alone.

### Key sources

Chapter 10 cites in the print book: D6, D61, D62, D63. Entries below are the sources this page draws on; some are related literature cited elsewhere in the book rather than in this chapter.

- D6 - Anthropic. (2024). Introducing the Model Context Protocol . [anthropic.com/news/model-context-protocol](https://www.anthropic.com/news/model-context-protocol)

- D12 - OpenAI. (2023). Function calling and other API updates . [openai.com/index/function-calling-and-other-api-updates/](https://platform.openai.com/docs/guides/function-calling)

### Primary-source links

- [Anthropic, "Introducing the Model Context Protocol" (November 25, 2024)](https://www.anthropic.com/news/model-context-protocol) - the launch announcement and the spec's authoritative starting point.

- [OpenAI, "Function calling and other API updates" (June 2023)](https://platform.openai.com/docs/guides/function-calling) - the predecessor pattern that established the tool-use call format MCP later generalized into a vendor-neutral protocol.

### Chapter contents

- What MCP is and what it is not (a transport, not a model; infrastructure, not computation).

- Why a protocol layer matters - the spinal-cord analog explained.

- The defensibility implication: tool calls in the audit trail give post-hoc decision reconstruction.

- Interop with the function-calling lineage and where MCP diverges.

### Live MCP catalog

                The current MCP server catalog - which vendors implement what, with which capabilities, and which client surfaces consume it - lives at [/mcp/](/mcp/). Each entry carries a verified date. Refreshed quarterly.