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What Is an AI Agent, Really?
June 2, 2026
An AI agent = LLM + Tools + Loop. If any of the three is missing, it is not an agent.
The Three Components
LLM — The reasoning engine. Given context and available tools, it decides what to do next. The LLM is NOT the agent. It is the brain of the agent.
Tools — The capability surface. Functions the agent can call: read files, run commands, search the web, query databases. Each tool has a name, description, and input schema.
Loop — The autonomous decision cycle. Think (LLM decides) leads to Act (tool executes) leads to Observe (result comes back) leads to Repeat.
What Each Combination Gives You
| Combination | Result |
|---|---|
| LLM only | Chatbot |
| LLM + Tools (no loop) | Augmented inference |
| LLM + Loop (no tools) | Talking to itself |
| LLM + Tools + Loop | Agent |
The Loop in Pseudocode
messages = [system_prompt, user_request]
while True:
response = llm.invoke(messages, tools=tool_definitions)
if response.is_final_answer:
print(response.content)
break
tool_name = response.tool_call.name
tool_args = response.tool_call.args
result = execute_tool(tool_name, tool_args)
messages.append(response)
messages.append(result)
Common Misconception
"The model is the agent." No. The model is the brain. The agent is the whole system: brain plus tools plus loop. A better brain helps, but better tools and a better loop help more.
From Module 1 of the Agentic Engineering Course. The full module includes your first lab: building a single-tool agent from scratch.