Agents & tools · Glossary term

What is ReAct?

An agent pattern that interleaves task reasoning, a concrete action, and an observation returned by the environment before deciding the next step.

Why does ReAct matter?

Environment feedback can correct assumptions and ground later decisions instead of forcing the model to complete the entire task from internal generation alone.

ReAct in practice

Expose a small set of typed tools, return concise observations, cap the loop, and verify the final artifact rather than storing private reasoning traces.

What is the common confusion about ReAct?

ReAct is a prompting and control pattern, not a guarantee of autonomy, correctness, or safe tool use.

Learn ReAct in the course

Lessons that name ReAct in a title or section

  • Few-Shot, Chain-of-Thought, Tree-of-Thought

    Telling a model what to do is prompting. Showing it how to think is engineering. The gap between 78% and 91% accuracy on the same model, same task, same data is not a better model.

    Phase 11: LLM Engineering

  • Agent State Machines — Graphs, Nodes, Checkpoints

    A ReAct loop written by hand is a while True. The same loop written as an explicit graph is something you can checkpoint, interrupt, branch, and time-travel through. The agent hasn't changed.

    Phase 11: LLM Engineering

  • The Agent Loop: Observe, Think, Act

    Every agent in 2026 is a variant of the ReAct loop from 2022 — Claude Code, Cursor, Devin, Operator included. Reasoning tokens interleave with tool calls and observations until a stop condition fires.

    Phase 14: Agent Engineering

Covered in Phase 11: LLM Engineering and Phase 14: Agent Engineering.

  • AgentA software system that lets a model select actions toward a goal, observe tool or environment results, and continue under an orchestration…
  • Function CallingA provider or application interface through which a model emits a structured request naming a tool and its arguments.
  • PlanningConstructing, selecting, or revising a sequence of actions and dependencies intended to move from the current state to a goal.
  • GroundingConnecting a generated answer or action to evidence, state, or observations that the system can identify and check.

Sources

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