The Harness Is the Thing

The author reflects on how AI-driven development tools have transformed software engineering, with the "harness"—a unified system for managing multiple LLM models and agents—becoming the critical infrastructure that bridges developer expectations and AI capabilities. By treating AI models as commodities and strategically layering cheaper models like Deepseek for routine tasks with frontier models for complex work, developers can now achieve enterprise-level productivity as solo practitioners. The key innovation is implementing a structured workflow (planner/worker/critic approach) within this harness rather than relying on any single tool's magic.