2.1Bridging Theory and Practice

The ReAct pattern is abstract: Observe, Think, Act, Evaluate. To make it concrete, we need to map each phase to actual commands that an AI agent can execute. The Playwright CLI (playwright-cli) — the 2026 default for agent-driven browser control — provides exactly these commands, making it a practical implementation of the ReAct loop for browser testing. (Vibium's vibe-check CLI, which earlier editions of this chapter used, implements the same mapping with a selector-based surface; the loop is identical.)