Old Zhang's AI Learning

Nov 9, 2026 · Artificial Intelligence

What Is a Harness? The LLM Execution Layer, Tool vs Data Planes, and ADE

This article explains Harness as the execution suite that lets LLMs act on code, detailing the five-layer architecture (LLM, Harness, Interface, MCP Data Plane, ADE), comparing tools like Claude Code, Codex, Pi, and T3 Code, and showing how MCP enables cross-harness orchestration for multi-model workflows.