📘 Introduction

The OpenAI Agent Builder is a visual, no-code canvas for creating intelligent workflows powered by AI. It lets you design and connect nodes — modular building blocks that define how your agent processes inputs, performs reasoning, calls external tools, applies safety checks, and produces outputs. Each node has a specific role, and together they shape how an agent thinks and acts.

In this ultimate guide, we’ll explore every node type available in OpenAI’s Agent Builder, explain how they work, and show how to combine them into powerful, flexible, and safe AI workflows.

💡 What Are Nodes?

In the OpenAI Agent Builder, nodes are the fundamental units of logic and control. Think of them as the “steps” your agent takes to complete a task — each node performs one clearly defined function, and connections between them control the sequence and flow of the workflow.

When you compose an agent, you insert nodes, configure them, and connect them to describe the process you want your agent to follow.

Here’s what makes nodes essential:

  • ⚙️ Modular building blocks — each node represents one task or action (e.g., get input, call a model, validate output, loop, transform data).
  • 🧩 Configurable — every node has settings (e.g., model parameters, variables, conditions).
  • 🔗 Composable — nodes connect to one another to form end-to-end logic chains.
  • 🖥️ Visual by design — in the Agent Builder canvas, nodes are represented as blocks with connectors showing data flow.
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In essence, nodes are the building blocks for agents — combining reasoning, tools, data, and safety into a single cohesive workflow.

🧩 Core Nodes

Core nodes are the foundation of every workflow. All flows begin with a Start node and include at least one Agent node.

🚀 Start

The Start node defines how your workflow receives input. In chat workflows, it does two key things:

  • Appends the user’s input to the conversation history.
  • Exposes an input_as_text variable representing the text input.

You can also add state variables to track global values throughout your workflow.

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Every workflow begins with one — and only one — Start node.

🤖 Agent

The Agent node is the heart of your workflow. It defines:

  • The model configuration (e.g., GPT model, temperature).
  • System instructions that guide the model’s behavior.
  • Tools that the agent can call.
  • Optional evaluations for testing and refinement.
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You can have multiple Agent nodes in one workflow. This allows you to split your logic into specialized agents — for example, one for rewriting, one for classification, and one for responding.

📝 Note

The Note node is purely informational. It doesn’t affect the workflow logic but helps document what’s happening.

Use it to:

  • Leave comments for your team.
  • Explain complex branches.
  • Add reminders or instructions.
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Think of it as sticky notes inside your workflow canvas.

🔧 Tool Nodes

Tool nodes let your agents interact with external systems — from file searches to APIs.

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