Agent Essentials

AI agents are rapidly transforming how modern software is built. But building capable agents requires more than simply calling an LLM API. This book provides a practical introduction to the concepts, architectures and frameworks behind modern AI agents.

You'll begin by exploring the evolution of agents and the architectural patterns used to build them. From there, the book covers practical aspects of working with frontier LLMs from OpenAI, Anthropic, Google, xAI and DeepSeek, including API access, authentication, security practices and cost management.

You'll then build agent-powered applications using LangChain and LlamaIndex, exploring memory, persistence, structured outputs, selective memory retrieval with BM25, tool integration through the Wikipedia API, and modern approaches to create UIs for agents.

By the end of the book, you will:

• Understand AI agent architectures and design patterns
• Learn LLM API fundamentals, security practices and cost control
• Access models from OpenAI, Anthropic, Google, xAI and DeepSeek
• Build agent applications with LangChain and LlamaIndex
• Add memory, persistence and structured outputs to agents
• Implement selective memory retrieval techniques using BM25
• Extend agent capabilities through external tools and APIs
• Build interactive agents with modern UIs