Designing Your Own AI Harness: A Deep Dive Into the Architecture of Agent Loops, Tools, Context, and Control

This article provides a comprehensive technical analysis of building custom AI agent harnesses, focusing on the architecture of agent loops, tools, context management, and control layers. It explains how improving the harness around a language model can significantly boost performance without changing the model itself. The author, a Head of Developer Relations at Dremio, covers first principles, model layers, tool design, context compaction, permission matrices, budgets, persistence, orchestration, evaluation, and anti-patterns. It targets engineers, product teams, and researchers who need to embed agents into applications or understand off-the-shelf agent internals. The article includes a staged build path from weekend demo to production-ready system.