The emergence of Agent-First Software Design

A new paradigm is emerging in software engineering where instead of writing explicit and discrete code for each task, engineers are providing instructions to AI agents that autonomously determine execution. This shift is illustrated by a project involving an AI-driven email secretary named Debra, which automates inbox management using a headless Claude Code SDK. Initially developed with traditional discrete scripts, the system was later restructured to use a single agent harness with access to necessary tools, allowing it to autonomously fetch emails, classify them, execute appropriate actions, and generate reports. This approach, which emphasizes instruction writing over rigid coding, offers greater adaptability and robustness, particularly in handling errors such as expired authentication tokens through natural language prompts rather than additional code. As AI models continue to improve, this agentic engineering method promises future-proofing by enabling systems to evolve with advancements without needing to modify the underlying code, potentially transforming all coding into instruction writing for long-running agents.