Stage 03 of 11 · Agent Fundamentals · 3 min · Reviewed Aug 2026
Agent Fundamentals: Autonomy, the Loop, Structured Output, Routing
This guide is how you build the first real agent: an observable loop, structured outputs you can parse, and routing so the expensive model is not used for every keystroke. It does not claim to show a model’s private chain-of-thought.
- Autonomy
- Agent loop
- Structured output
- Routing
What you learn
How to build your first agent as an inspectable loop, not a longer prompt.
Autonomy has a boundary
An agent is autonomous inside a sandbox you define: which tools, which data, which budget, which stop. Outside that fence it should not act. “Autonomous” is not “unsupervised on production.”
Write the boundary down: allowed tools, max steps, max tokens, max spend, human gates for irreversible actions. If you cannot name the fence, you do not have an agent. You have a demo.
The observable loop
Most useful agents share the same public events: receive a task, optionally plan, select a tool, call it, receive an observation, update state, verify, then output or fail. If a product cannot show those events, it is hard to trust and hard to teach.
The model proposes. Tools execute. The environment returns observations. The run ends when a stop condition is met or an error is unrecoverable. That is the whole agent.
Interactive
The Core Agent Loop
Receive task
The agent receives a user task or goal with defined success criteria and a budget.