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.

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From Module 1 of the Agentic Engineering Course. The full module includes your first lab: building a single-tool agent from scratch.