---
title: "Model Context Protocol (MCP) Architecture Specification"
canonical: "https://mcp-codex.com/protocol"
source: "MCP Codex (https://mcp-codex.com)"
dateModified: "2026-09-28"
---

# Model Context Protocol (MCP) Architecture Specification

The open standard for connecting AI models to context repositories, external execution tools, and enterprise databases.

## Architecture Summary
- **Client**: Host application orchestrating LLM interactions (Claude Desktop, Cursor, OpenAI Codex, Windsurf, Antigravity).
- **Server**: Exposes tools, prompts, and resources over JSON-RPC 2.0.
- **Transports**:
  1. `stdio`: Standard Input/Output communication over OS processes. Ideal for local filesystem and secure sandbox tools.
  2. `SSE` (Server-Sent Events): HTTP transport for cloud-hosted and multi-tenant services.

## Core Primitives
1. **Tools**: Executable functions callable by the model (`tools/list`, `tools/call`).
2. **Resources**: Read-only contextual data documents (`resources/list`, `resources/read`).
3. **Prompts**: Standardized workflow templates and reusable system directives (`prompts/list`, `prompts/get`).

## Canonical Reference
- Specification URL: https://mcp-codex.com/protocol
- Agent Index: https://mcp-codex.com/api/agent/index
- Manifest: https://mcp-codex.com/llms.txt