Prompt engineering, context engineering, loop engineering, and harness engineering are four distinct layers of the same system, each answering a different question about getting reliable behavior from a model, according to HackerNoon. Prompt engineering optimizes a single message—phrasing, examples, step-by-step reasoning requests, and output format—and lives entirely inside one turn; its typical failure is a vague or misread answer to a single message. Context engineering concerns what information the model has in front of it, including retrieved documents, conversation history, tool definitions, memory files, and results from other tools; its typical failure is being confident, fluent, and wrong because data was missing, stale, or buried. Loop engineering addresses what should happen across steps and when the task is done; its typical failure is spinning in circles, never finishing, or declaring victory too early. Harness engineering covers the machinery that makes each step run reliably; its typical failure is a tool failing silently, a retry never firing, or nobody noticing. The article summarizes: wording is the prompt, knowledge is the context, steps and stopping are the loop, and plumbing is the harness.