A year ago, Simon Willison wrote one of the cleanest definitions of an agent that has stuck around: An LLM agent runs tools in a loop to achieve a goal. That definition stuck because it describes what every production agent actually does. Kiro, Amazon Q Developer, Quick Agents, Codex, Claude Code: under the hood, they all run the same shape. The agent loop is the common denominator. But the loop was never the hard part. The hard part was everything around it. Pick a framework. Wire up tools. Pro