Library › Book 3 › The ReAct Core Loop
The ReAct Core Loop
2.1🔒The Four PhasesThe ReAct loop has four phases that repeat until the test objective is met or a guardrail is triggered:
2.2🔒A Complete ReAct Agent ImplementationHere is the complete implementation that ties all four phases together:
2.3🔒Why Each Phase MattersThe four phases create a feedback loop that enables capabilities deterministic scripts cannot match:
2.4🔒The History BufferThe history buffer is critical for preventing infinite loops and enabling learning within a test run.
2.5🔒Limitations of the ReAct Pattern1. Non-deterministic. The same test objective may take different paths on different runs. 2. Expensive. Each step requires an LLM call. A…
2.6🔒When to Use ReAct vs. Scripts
2.7🔒ReAct in Production Tools (as of July 2026)The loop you just learned is not something you will only ever build by hand. It is the engine inside the production agentic tooling that…
2.8🔒Career Translation- Designed and implemented ReAct-pattern test agents with four-phase observe-think-act-evaluate loops, achieving adaptive test execution…
2.9🔒Q&AInterview Depth CheckPrompt: You deploy a ReAct agent and it keeps clicking the same broken button 15 times in a row before timing out. What is the root cause…