---
title: "Middleware"
description:
  "Connect to existing protocols, in process agents or custom solutions via
  AG-UI"
---

# Introduction

A middleware implementation allows you to **translate existing protocols and
applications to AG-UI events**. This approach creates a bridge between your
existing system and AG-UI, making it perfect for adding agent capabilities to
current applications.

## When to use a middleware implementation

Middleware is the flexible option. It allows you to translate existing protocols
and applications to AG-UI events creating a bridge between your existing system
and AG-UI.

Middleware is great for:

- Taking your **existing protocol or API** and **translating it universally**
- Working within the confines of **an existing system or framework**
- **When you don't have direct control** over the agent framework or system

## What you'll build

In this guide, we'll create a middleware agent that:

1. Extends the `AbstractAgent` class
2. Connects to OpenAI's GPT-4o model
3. Translates OpenAI responses to AG-UI events
4. Runs in-process with your application

This approach gives you maximum flexibility to integrate with existing codebases
while maintaining the full power of the AG-UI protocol.

Let's get started!

## Prerequisites

Before we begin, make sure you have:

- [Node.js](https://nodejs.org/) **v16 or later**
- An **OpenAI API key**

### 1. Provide your OpenAI API key

First, let's set up your API key:

```bash
# Set your OpenAI API key
export OPENAI_API_KEY=your-api-key-here
```

### 2. Install build utilities

Install the following tools:

```bash
brew install protobuf
```

```bash
npm i nx
```

```bash
curl -fsSL https://get.pnpm.io/install.sh | sh -
```

## Step 1 – Scaffold your integration

Start by cloning the repo

```bash
git clone git@github.com:ag-ui-protocol/ag-ui.git
cd ag-ui/
```

Copy the middleware-starter template to create your OpenAI integration:

```bash
cp -r integrations/middleware-starter integrations/openai
```

### Update metadata

Open `integrations/openai/package.json` and update the fields to match your new
folder:

```json
{
  "name": "@ag-ui/openai",
  "author": "Your Name <your-email@example.com>",
  "version": "0.0.1",

  ... rest of package.json
}
```

Next, update the class name inside `integrations/openai/src/index.ts`:

```ts
// change the name to OpenAIAgent
export class OpenAIAgent extends AbstractAgent {}
```

Finally, introduce your integration to the dojo by adding it to
`apps/dojo/src/menu.ts`:

```ts
// ...
export const menuIntegrations: MenuIntegrationConfig[] = [
  // ...

  {
    id: "openai",
    name: "OpenAI",
    features: ["agentic_chat"],
  },
];
```

And `apps/dojo/src/agents.ts`:

```ts
// ...

export const agentsIntegrations: AgentIntegrationConfig[] = [
  // ...

  {
    id: "openai",
    agents: async () => {
      return {
        agentic_chat: new OpenAIAgent(),
      };
    },
  },
];
```

## Step 2 – Add package to dojo dependencies

Open `apps/dojo/package.json` and add the package `@ag-ui/openai`:

```json
{
  "name": "demo-viewer",
  "version": "0.1.0",
  "private": true,
  "scripts": {
    "dev": "next dev",
    "build": "next build",
    "start": "next start",
    "lint": "next lint"
  },
  "dependencies": {
    "@ag-ui/agno": "workspace:*",
    "@ag-ui/langgraph": "workspace:*",
    "@ag-ui/mastra": "workspace:*",
    "@ag-ui/middleware-starter": "workspace:*",
    "@ag-ui/server-starter": "workspace:*",
    "@ag-ui/server-starter-all-features": "workspace:*",
    "@ag-ui/vercel-ai-sdk": "workspace:*",
    "@ag-ui/openai": "workspace:*", <- Add this line

  ... rest of package.json
}
```

## Step 3 – Start the dojo

Now let's see your work in action:

```bash
# Install dependencies
pnpm install

# Compile the project and run the dojo
pnpm dev
```

Head over to [http://localhost:3000](http://localhost:3000) and choose
**OpenAI** from the drop-down. You'll see the stub agent replies with **Hello
world!** for now.

Here's what's happening with that stub agent:

```ts
// integrations/openai/src/index.ts
  AbstractAgent,
  BaseEvent,
  EventType,
  RunAgentInput,
} from "@ag-ui/client"

export class OpenAIAgent extends AbstractAgent {
  run(input: RunAgentInput): Observable<BaseEvent> {
    const messageId = Date.now().toString()
    return new Observable<BaseEvent>((observer) => {
      observer.next({
        type: EventType.RUN_STARTED,
        threadId: input.threadId,
        runId: input.runId,
      } as any)

      observer.next({
        type: EventType.TEXT_MESSAGE_START,
        messageId,
      } as any)

      observer.next({
        type: EventType.TEXT_MESSAGE_CONTENT,
        messageId,
        delta: "Hello world!",
      } as any)

      observer.next({
        type: EventType.TEXT_MESSAGE_END,
        messageId,
      } as any)

      observer.next({
        type: EventType.RUN_FINISHED,
        threadId: input.threadId,
        runId: input.runId,
      } as any)

      observer.complete()
    })
  }
}
```

## Step 4 – Bridge OpenAI with AG-UI

Let's transform our stub into a real agent that streams completions from OpenAI.

### Install the OpenAI SDK

First, we need the OpenAI SDK:

```bash
cd integrations/openai
pnpm install openai
```

### AG-UI recap

An AG-UI agent extends `AbstractAgent` and emits a sequence of events to signal:

- lifecycle events (`RUN_STARTED`, `RUN_FINISHED`, `RUN_ERROR`)
- content events (`TEXT_MESSAGE_*`, `TOOL_CALL_*`, and more)

### Implement the streaming agent

Now we'll transform our stub agent into a real OpenAI integration. The key
difference is that instead of sending a hardcoded "Hello world!" message, we'll
connect to OpenAI's API and stream the response back through AG-UI events.

The implementation follows the same event flow as our stub, but we'll add the
OpenAI client initialization in the constructor and replace our mock response
with actual API calls. We'll also handle tool calls if they're present in the
response, making our agent fully capable of using functions when needed.

```typescript
// integrations/openai/src/index.ts
  AbstractAgent,
  RunAgentInput,
  EventType,
  BaseEvent,
} from "@ag-ui/client"


export class OpenAIAgent extends AbstractAgent {
  private openai: OpenAI

  constructor(openai?: OpenAI) {
    super()
    // Initialize OpenAI client - uses OPENAI_API_KEY from environment if not provided
    this.openai = openai ?? new OpenAI()
  }

  run(input: RunAgentInput): Observable<BaseEvent> {
    return new Observable<BaseEvent>((observer) => {
      // Same as before - emit RUN_STARTED to begin
      observer.next({
        type: EventType.RUN_STARTED,
        threadId: input.threadId,
        runId: input.runId,
      } as any)

      // NEW: Instead of hardcoded response, call OpenAI's API
      this.openai.chat.completions
        .create({
          model: "gpt-4o",
          stream: true, // Enable streaming for real-time responses
          // Convert AG-UI tools format to OpenAI's expected format
          tools: input.tools.map((tool) => ({
            type: "function",
            function: {
              name: tool.name,
              description: tool.description,
              parameters: tool.parameters,
            },
          })),
          // Transform AG-UI messages to OpenAI's message format
          messages: input.messages.map((message) => ({
            role: message.role as any,
            content: message.content ?? "",
            // Include tool calls if this is an assistant message with tools
            ...(message.role === "assistant" && message.toolCalls
              ? {
                  tool_calls: message.toolCalls,
                }
              : {}),
            // Include tool call ID if this is a tool result message
            ...(message.role === "tool"
              ? { tool_call_id: message.toolCallId }
              : {}),
          })),
        })
        .then(async (response) => {
          const messageId = Date.now().toString()

          // NEW: Stream each chunk from OpenAI's response
          for await (const chunk of response) {
            // Handle text content chunks
            if (chunk.choices[0].delta.content) {
              observer.next({
                type: EventType.TEXT_MESSAGE_CHUNK, // Chunk events open and close messages automatically
                messageId,
                delta: chunk.choices[0].delta.content,
              } as any)
            }
            // Handle tool call chunks (when the model wants to use a function)
            else if (chunk.choices[0].delta.tool_calls) {
              let toolCall = chunk.choices[0].delta.tool_calls[0]

              observer.next({
                type: EventType.TOOL_CALL_CHUNK,
                toolCallId: toolCall.id,
                toolCallName: toolCall.function?.name,
                parentMessageId: messageId,
                delta: toolCall.function?.arguments,
              } as any)
            }
          }

          // Same as before - emit RUN_FINISHED when complete
          observer.next({
            type: EventType.RUN_FINISHED,
            threadId: input.threadId,
            runId: input.runId,
          } as any)

          observer.complete()
        })
        // NEW: Handle errors from the API
        .catch((error) => {
          observer.next({
            type: EventType.RUN_ERROR,
            message: error.message,
          } as any)

          observer.error(error)
        })
    })
  }
}
```

### What happens under the hood?

Let's break down what your agent is doing:

1. **Setup** – We create an OpenAI client and emit `RUN_STARTED`
2. **Request** – We send the user's messages to `chat.completions` with
   `stream: true`
3. **Streaming** – We forward each chunk as either `TEXT_MESSAGE_CHUNK` or
   `TOOL_CALL_CHUNK`
4. **Finish** – We emit `RUN_FINISHED` (or `RUN_ERROR` if something goes wrong)
   and complete the observable

## Step 4 – Chat with your agent

Reload the dojo page and start typing. You'll see GPT-4o streaming its answer in
real-time, word by word.

## Bridging AG-UI to any protocol

The pattern you just implemented—translate inputs, forward streaming chunks,
emit AG-UI events—works for virtually any backend:

- REST or GraphQL APIs
- WebSockets
- IoT protocols such as MQTT

## Connect your agent to a frontend

Tools like [CopilotKit](/) already understand AG-UI and
provide plug-and-play React components. Point them at your agent endpoint and
you get a full-featured chat UI out of the box.

## Share your integration

Did you build a custom adapter that others could reuse? We welcome community
contributions!

1. Fork the [AG-UI repository](https://github.com/ag-ui-protocol/ag-ui)
2. Add your package under `integrations`. See
   [Contributing](../development/contributing) for more details and naming
   conventions.
3. Open a pull request describing your use-case and design decisions

If you have questions, need feedback, or want to validate an idea first, start a
thread in the GitHub Discussions board:
[AG-UI GitHub Discussions board](https://github.com/orgs/ag-ui-protocol/discussions).

Your integration might ship in the next release and help the entire AG-UI
ecosystem grow.

## Conclusion

You now have a fully-functional AG-UI adapter for OpenAI and a local playground
to test it. From here you can:

- Add tool calls to enhance your agent
- Publish your integration to npm
- Bridge AG-UI to any other model or service

Happy building!
