Building an agent from scratch is easy for the first demo. It gets harder when you need to run it reliably. The model call is only one part of the system. You still need tool dispatch, state management, retries, tracing, human approval, memory, evaluation hooks, and a clear way to stop the loop.

Agent frameworks give you reusable pieces for that infrastructure: tool calling, graph execution, checkpointing, multi-agent handoffs, observability, and workflow orchestration. They can save time, but they also shape how your system is built. A framework is a trade-off. It does not remove the need to understand how agents work.

This chapter compares common framework styles and gives you a practical way to decide when to use one, when to build directly, and which patterns matter either way.