In the last post we covered how an agent perceives — how webhooks feed it events and how the context window works like a limited routing table. Perception only gets an agent halfway there, though. The real question is what it does with that information once it has it. That's where the ReAct pattern comes in, and if you've ever worked a ticket the "right" way instead of just guessing, you already understand it intuitively.
The three-step loop you already use every day
Picture a ticket landing on your desk: "Users are reporting slow network performance." A junior engineer might restart something and hope for the best. An experienced one runs a mental loop instead:
- Think — "Users report slow performance. Before I touch anything, let me check the router status."
- Act — Actually run
show interface, check CPU, pull the logs. - Observe — "Router R12 CPU usage is 97%." New information is now on the table.
- Think again — "That CPU number explains the symptom. What's driving CPU that high — a routing loop, a process leak, an attack?"
That repeating cycle — reason, act, observe, reason again — is exactly what the ReAct pattern (Reason + Act) gives an AI agent. It isn't a coincidence that it maps so cleanly onto troubleshooting methodology; ReAct was built to give language models the same discipline a good engineer already has: don't act blindly, and don't just theorize without checking your work.
Here's what that loop looks like laid out:
Why this beats the two approaches that came before it
Before ReAct, agent-style systems generally fell into one of two buckets, and if you've dealt with older automation tooling, you've probably run into both.
Reasoning-only systems could analyze a problem and tell you what should be done — but they had no hands. Think of a chatbot that can explain that "high CPU is usually caused by a routing process or a control-plane flood" but can't actually go check your router. Useful for a second opinion, useless for getting the job done.
Acting-only systems could execute, but with zero judgment in the loop. This is your classic runbook script or blind automation: it fires a fixed sequence of commands whether or not the situation actually calls for them. It's fast, but it can't adapt when the ticket doesn't match the script.
ReAct fuses both halves. Reasoning decides which action makes sense given the current situation; the action then produces new, real information; and that new information reshapes the next round of reasoning. Each loop iteration is smarter than the last because it's grounded in something that actually happened, not just a guess. That grounding is the entire point — it's the difference between a script that blindly restarts a service and an agent that checks CPU first, correlates it with a config change timestamp, and only then decides what to do.
Chain-of-Thought: the reasoning made visible
You'll often see ReAct mentioned alongside Chain-of-Thought (CoT) prompting, and it's worth knowing the difference because they solve related but distinct problems.
Without CoT, a model tends to jump straight to an answer — the AI equivalent of an engineer saying "just reboot it" with no explanation. With CoT, the model is nudged to lay out its reasoning step by step before acting, the same way a good engineer talks through their logic on a bridge call instead of just typing commands silently: "CPU is high, that could be a process or a flood, let me check show processes cpu before I decide anything."
The payoff is the same one you'd expect from any engineer who explains their thinking out loud: it's easier to trust, easier to audit, and a lot easier to catch a bad assumption before it turns into a bad action.
Reading agent traces: your new show-tech
If you're going to work with agents day to day, there's one practical skill worth building early: reading a trace.
A trace is simply a structured log of everything the agent did — every Think step, every Act step, every Observe step, nested in order. Tools like LangSmith display these as a tree: a parent run (the overall task) containing child runs, where each child is either an LLM call (reasoning happened here) or a tool call (an action happened here).
If that sounds familiar, it should — it's not far from reading a show tech-support bundle or unpacking a nested syslog trace to figure out what a device actually did and in what order. The skill transfers almost directly: find where the reasoning went wrong, or find where the tool call returned something unexpected, and you've found your root cause.
One caution worth keeping in mind
Reasoning traces make an agent more explainable, but explainable isn't the same as infallible. A model can lay out confident, well-structured reasoning and still act on a flawed assumption — the AI version of an engineer who sounds certain but is troubleshooting the wrong VLAN. Treat agent reasoning the way you'd treat a junior engineer's diagnosis: useful, often correct, but worth a second look before it touches anything production-critical.
Quick recap
- ReAct = Think → Act → Observe, repeated until the agent has a final answer — the same loop experienced engineers already run mentally when troubleshooting.
- It replaces two older, weaker patterns: reasoning-only systems that can't act, and acting-only systems that can't think.
- Chain-of-Thought prompting is what makes the "Think" step explicit and auditable, rather than a hidden jump to a conclusion.
- Traces are your debugging tool for agent behavior — read them the way you'd read a nested log bundle.
- Confident reasoning is not the same as correct reasoning — verify before letting an agent touch anything critical.
FAQ
- The agent is using Chain-of-Thought
prompting to generate random responses and the tool output appears in the
Action step.
- The agent is using the ReAct pattern
(Reason → Act → Observe), Chain-of-Thought prompting to explain its
reasoning, and the tool’s output appears in the Observation step.
- The agent is following a rule-based system
and the Observation step contains the system prompt instructions.
- The agent is using ReAct but
Chain-of-Thought prevents the agent from calling tools.
Ans - The agent is using the ReAct pattern (Reason →
Act → Observe), Chain-of-Thought prompting to explain its reasoning, and the
tool’s output appears in the Observation step.
This post continues the series on how AI agents work. Catch up on the earlier piece on how agents gather information before they ever start reasoning:
Related Reading on Networklearner:
- AI Agent Perception and Context Windows Explained for Network Engineers
- Understanding AI Agents for Network Engineers: LLMs, Prompts, Tokens and Context Explained
- Agentic AI for Network Engineers: What It Actually Means
- Reactive Automation vs Generative AI vs Agentic AI in Networking
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