ReAct (Reason + Act)
Industry Definition Set • Entity Resolution Path: /glossary/react
Quick Answer / TL;DR
A framework that interleaves reasoning (thinking) and acting (tool calling) in LLM agents, enabling more robust and interpretable problem-solving.
Key Takeaways
- Interleaves reasoning and action in agent workflows.
- Produces more interpretable and robust agent behavior.
- Naturally maps to MCP tool-calling patterns.
- Reduces hallucination by grounding actions in reasoning.
Definitive Statement: A framework that interleaves reasoning (thinking) and acting (tool calling) in LLM agents, enabling more robust and interpretable problem-solving.
Technical Context & Protocol Usage
- Detailed Explanation
- ReAct combines chain-of-thought reasoning with action execution. The model alternates between thought steps (reasoning about the current state) and action steps (calling tools or taking actions). This pattern is fundamental to modern AI agents and is well-supported by MCP, where each action step corresponds to an MCP tool call.
Format & Payload Metadata
Format: Alternating thought and action steps in prompt
Latency: Increases interaction rounds; improves accuracy
Real-World Implementation Use Case
An agent uses ReAct to reason about a user's request, call an MCP `search` tool, reason about the results, then call a `summarize` tool before answering.
Cite This Page
MLA Style:
MCPserver.in Engineering. "ReAct (Reason + Act)." MCPserver.in Knowledge Hub, 20 July 2026, mcpserver.in/glossary/react.
Related Terms
Model Context Protocol (MCP)
An open, secure protocol that standardizes how artificial intelligence agents and large language models (LLMs) exchange context, tools, prompts, and data resources with external servers.
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Stdio Transport (Standard Input/Output)
A local-only transport mechanism where the AI client spawns the MCP server as a child process and communicates via standard input (stdin) and standard output (stdout) channels.
SSE Transport (Server-Sent Events)
A lightweight, unidirectional HTTP-based streaming protocol used by remote MCP servers to push messages to AI clients, with client-to-server writes sent over standard POST requests.
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