Build an AI Agent from Scratch: 50 Lines of Python to Understand Core Concepts

Build a thinking, tool-using AI agent in pure Python + OpenAI API - zero frameworks, 50 lines, complete understanding.

💡 What You Will Learn

Build a thinking, tool-using AI agent in pure Python + OpenAI API - zero frameworks, 50 lines, complete understanding.

The Agent Core Loop

1. Receive user input
2. LLM decides: answer directly or use a tool?
3. If tool needed -> call tool -> feed result to LLM -> back to step 2
4. If direct answer -> output to user

def run_agent(user_input):
    messages = [{'role': 'user', 'content': user_input}]
    for _ in range(5):
        response = client.chat.completions.create(
            model='gpt-4o-mini', messages=messages, tools=tools)
        msg = response.choices[0].message
        if msg.tool_calls:
            # execute tool
            pass
        else:
            return msg.content

Agent = LLM + Tools + Loop. Master these 50 lines and any framework becomes just configuration.