What Is Context Engineering? The Next Skill After Prompts, and How to Beat "Context Rot"
The center of gravity in working with AI is shifting from prompt engineering to context engineering. Borrowing Anthropic's definition, context engineering is "the set of strategies for curating and maintaining the optimal set of tokens (information) you hand the model during inference" — covering not just the prompt but everything in the context window: the system prompt, tools, conversation history, and external data. It matters because of "context rot": the more tokens you add, the more accuracy actually drops. Chroma's 2025 study tested 18 leading models (GPT, Claude, Gemini, and more) and every one degraded as input grew, with information in the middle of long contexts especially easy to overlook ("lost in the middle"). This beginner-friendly guide covers what context engineering is and how it relates to prompt engineering, why context rot happens (attention is a finite budget), what actually lives in the context, six core techniques (right-altitude instructions, tool curation, just-in-time retrieval, compaction/summary compression, external memory notes, and sub-agent isolation), how it relates to RAG and Claude Skills, and habits you can use today such as starting a new session when the topic changes and pasting only the key points. The core idea: keep only the smallest, highest-signal tokens.