From Prompt Writing to Context Design: An In-Depth Look at Context Engineering

The concept of prompt engineering, as it was understood in 2025, has become obsolete. Today’s agent-based tools, such as Claude Code and Codex, reveal that a mere fraction of the context—around 0.03%—is derived from user input. The majority of the context is shaped by system prompts, memory, skills, and historical data. These elements are designed to maximize resource usage and can significantly impact costs. This shift emphasizes the need for a deeper understanding of context design, moving beyond simple prompts to a more comprehensive approach that integrates various components of interaction.