Fundamentals
What makes a system agentic, the agent loop, and what agentic engineers actually build.
A system is agentic when a model decides which action to take next based on what it observed, inside a loop with a termination condition — everything else is a program with an LLM in it.
Every agent is the same loop — observe, reason, choose an action, run a tool, fold the result into state, check for completion — and every production problem lives in one of those boxes.
Six recurring system types — assistants, RAG, tool-calling systems, process automation, multi-agent systems, and the evaluation/observability layer that makes the others shippable.
Conversational, support, research, coding and internal assistants share one shape and differ on four axes — knowledge, tools, risk and latency — which decide the architecture.
Agents orchestrating APIs, databases, documents and humans replace glue work — but side effects demand idempotency, audit trails, and often a workflow engine instead of an agent.
Escalate plain code → LLM call → structured output → tool calling → RAG → workflow → agent → multi-agent one rung at a time, and stop at the first rung that solves the problem.