What is ReAct?
ReAct (Reasoning and Acting) is an agent paradigm that interleaves reasoning steps (thinking through what to do and why) with action steps (using tools or taking actions), creating a more interpretable and effective decision-making process. Rather than jumping directly to actions or completing all reasoning upfront, ReAct agents alternate between thinking about the task, taking actions, observing results, and reasoning about what to do next based on those observations.
The pattern typically involves the agent explicitly verbalizing its reasoning in "thought" steps where it analyzes the current situation, determines what information is needed or what action would be helpful, and explains its reasoning. This is followed by an "action" step where the agent uses a tool or takes a specific action. The result of that action becomes an "observation" that feeds into the next reasoning step, creating an iterative loop of thought-action-observation that continues until the task is complete.
ReAct has become influential in agent design because it combines the benefits of chain-of-thought reasoning with the capability to interact with external tools and environments. The explicit reasoning steps make agent behavior more interpretable and debuggable, while the action steps ground the reasoning in real information and tool use. Many modern agent frameworks implement ReAct-style patterns, and research has shown that this interleaving of reasoning and acting generally outperforms approaches that separate planning from execution or that act without explicit reasoning steps.