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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 ​

python

    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.