Definition
Agent
An agent is an LLM given access to external knowledge through RAG, the ability to take actions through tool calling, or both. The book's formula: LLM plus RAG and/or tools equals agent. RAG supplies knowledge the model was not trained on; tools give it hands to send email, query APIs, or run code. Most production agents are exactly this: a model, a retriever, and a handful of tools.
Explained in
Chapter 9: What Is an Agent?
The moment you give an LLM access to knowledge or tools, it becomes an agent. And that makes all the difference.
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