What Is an AI Agent?

An AI agent is an AI system that autonomously perceives its environment, makes decisions, and takes action toward a given goal. Unlike traditional AI that simply answers questions, agents can plan and execute tasks across multiple steps — a fundamental difference from conventional AI.

Target audience: Those who want to understand the basics of AI and LLMs, or who have heard the term “AI agent” but want to learn more.

Estimated learning time: 15 minutes to read

Prerequisites: What Is Deep Learning?

What Is an AI Agent?

An AI agent is an AI system that, when given a goal, autonomously creates a plan to achieve it and executes multi-step actions using tools.

Traditional AI returns a single output for a single input. An AI agent, by contrast, receives a goal, figures out the necessary steps on its own, and keeps acting until it produces a result — a fundamentally different approach.

AI Agents vs. Traditional AI

Aspect	Traditional AI (Chatbot)	AI Agent
Execution model	One question → one answer	Goal → multi-step execution
Tool use	None or limited	Autonomously uses diverse tools: search, code execution, file operations, etc.
State management	Conversation history only	Manages working state, progress, and intermediate results
Decision-making	Responds according to user instructions	Decides what to do next on its own
Typical example	Answering “What’s the weather tomorrow?”	Executing “Create a competitor analysis report”

Understanding Through Analogy

A traditional chatbot is like a front-desk receptionist. It answers questions, but for complex procedures you have to walk to each department yourself.

An AI agent is more like a capable personal assistant. Just say “Prepare a presentation for next week,” and it autonomously handles information gathering, outlining, drafting, and reviewing.

The Four Components of an AI Agent

AI agents are made up of four elements.

graph TD
    Goal["Goal\nUser instruction"] --> LLM

    subgraph Agent["AI Agent"]
        LLM["LLM Core\nThinking · Planning · Judgment"]
        Memory["Memory\nShort-term · Long-term"]
        Orchestration["Orchestration\nLogic"]
        LLM <--> Memory
        LLM --> Orchestration
    end

    subgraph Tools["Tools"]
        Search["Web Search"]
        Code["Code Execution"]
        File["File Operations"]
        Browser["Browsing"]
        API["External API"]
    end

    Orchestration --> Tools
    Tools --> Orchestration

1. LLM Core (Thinking & Planning)

The LLM (Large Language Model) acts as the agent’s “brain.” It receives the goal, thinks about “what to do next,” and generates instructions to call tools.

Current agents commonly use GPT-4o (OpenAI), Claude 3.5 Sonnet / Claude 3.7 Sonnet (Anthropic), and Gemini 1.5 Pro (Google).

2. Tools (Connection to the Outside World)

Tools are the means by which the agent actually “acts.” Since the LLM core alone cannot perform knowledge retrieval, file operations, or code execution, it interacts with the external environment through tools.

Tool Type	Examples
Information retrieval	Web search, Wikipedia lookup, database queries
Computer operations	Code execution, file read/write, command execution
Browsing	Viewing web pages, scraping
External services	Sending emails, calendar operations, GitHub operations

3. Memory

The mechanism by which an agent stores and retrieves information.

Type	Description	Example
Short-term memory	Working state during the current task	Conversation history, most recent tool execution results
Long-term memory	Information retained across tasks	User preferences, past task results, documents

4. Orchestration Logic

The control layer that manages when and in what order to call tools, and whether parallel execution is possible. In multi-agent systems where multiple agents collaborate, this logic plays a central role. See Orchestration for details.

How the ReAct Loop Works

ReAct (Reason + Act) is a widely used action principle for AI agents. By repeating “Think → Act → Observe,” it solves complex tasks step by step.

graph LR
    Goal["Receive Goal"] --> Reason

    Reason["Reason\n(Think · Plan)\nDecide what to do next"]
    Act["Act\n(Action)\nCall a tool"]
    Observe["Observe\n(Observation)\nCheck the result"]

    Reason --> Act
    Act --> Observe
    Observe --> Reason

    Observe -->|"Goal achieved?"| Done["Done\nGenerate final answer"]

Step Descriptions

Reason (Thinking): The LLM infers “what to do next” based on the goal and current state. Example: “First, get the latest information via web search.”
Act (Action): Calls the decided tool. Example: “Execute Python code to calculate.”
Observe (Observation): Receives the tool’s execution result and checks whether progress has been made toward the goal.
This cycle repeats until the goal is achieved, then a final answer is generated.

Concrete Example: Research Report Task

Let’s look at the steps an agent executes after receiving the instruction: “Please create a report on the latest trends in the EV (electric vehicle) market.”

Goal: Create a report on the latest EV market trends

[Reason] I need to research the market share of major players first
[Act]    Web search tool: "EV market share 2026"
[Observe] Search results: Tesla 18%, BYD 22%, others...

[Reason] I also need trend data on sales volume
[Act]    Web search tool: "EV sales volume 2025-2026 statistics"
[Observe] Search results: 2025, 35% year-over-year growth...

[Reason] Let me also research the Japanese market
[Act]    Web search tool: "Japan EV adoption rate 2026"
[Observe] Search results: adoption rate 12%, charging infrastructure challenges...

[Reason] I now have enough information. Let me structure the report.
[Act]    Code execution tool: graph generation script
[Observe] Graph image generated

[Done]   Generate and submit the report

Information gathering, organizing, and writing that would take a human several hours — an agent executes autonomously.

Why AI Agents Are Practical in 2026

There are three main reasons why AI agents rapidly became practical between 2024 and 2026.

1. Improved LLM Capabilities

Modern LLMs (Claude 3.7 Sonnet, GPT-4o, etc.) can now perform complex reasoning, planning, and tool-use decisions with high accuracy — far beyond simple text generation. The performance of the “brain” executing the ReAct loop has improved dramatically.

2. Standardization of Tool Integration (MCP)

The MCP (Model Context Protocol) standard has spread, allowing agents to interact with a wide variety of external tools in a unified way. See AI Agents and MCP for details.

3. Cost Reduction and API Maturity

The cost of LLM API usage has dropped significantly compared to 2022, making it economically feasible for agents to make many LLM calls. Major providers have also standardized agent-oriented features such as Function Calling and Tool Use.

Summary

An AI agent is an AI system that autonomously perceives, decides, and acts toward its environment
The biggest difference from traditional chatbots is “autonomous multi-step execution”
Four components: LLM core, tools, memory, and orchestration logic
The ReAct loop (Reason → Act → Observe) solves complex tasks incrementally
As of 2026, agents have entered the practical stage due to improved LLMs, MCP standardization, and cost reduction

Frequently Asked Questions

Q: What’s the difference between an AI agent and a chatbot?

A: A chatbot returns one answer for one question. An AI agent receives a goal and autonomously executes tasks across multiple steps using tools. A chatbot is a “passive responder”; an agent is an “active executor.”

Q: Do I need programming knowledge to use AI agents?

A: To simply use pre-built agent tools (Claude Code, Devin, AutoGPT, etc.), no programming knowledge is required. Python or TypeScript knowledge is helpful if you want to build or customize your own agent.

Q: Do AI agents operate completely autonomously? What about safety?

A: It depends on the design. Many systems incorporate a “Human-in-the-loop” mechanism that asks for human confirmation before important decisions (such as deleting files or sending emails). For irreversible operations and high-risk decisions, setting up human approval steps is best practice.

Q: What does “ReAct” stand for?

A: It’s a portmanteau of “Reasoning” and “Acting.” It was proposed in the paper “ReAct: Synergizing Reasoning and Acting in Language Models,” published by Google researchers in 2022.

References

Next step: AI Agent Orchestration