---
description: Handle real-time output from commands and processes with the Sandbox SDK 0.x.
title: Stream output
image: https://developers.cloudflare.com/sandbox/sdk/guides/streaming-output/og.png?v=4215925b9324a1f3
---

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> Use this file to discover all available pages before exploring further.

# Stream output

Last updated Sep 30, 2026|Copy as Markdown| [View as Markdown](https://developers.cloudflare.com/sandbox/sdk/guides/streaming-output/index.md)| [Agent setup](https://developers.cloudflare.com/agent-setup/)

Note

This page documents Sandbox SDK 0.x for existing applications. For new applications, refer to [Stream command output](https://developers.cloudflare.com/sandbox/commands/stream-command-output/). To move an existing application to `@cloudflare/sandbox` 1.0, refer to [Migrate from Sandbox SDK 0.x](https://developers.cloudflare.com/sandbox/sdk/migrate/).

This guide shows you how to handle real-time output from commands, processes, and code execution.

## When to use streaming

Use streaming when you need:

- **Real-time feedback** - Show progress as it happens
- **Long-running operations** - Builds, tests, installations that take time
- **Interactive applications** - Chat bots, code execution, live demos
- **Large output** - Process output incrementally instead of all at once
- **User experience** - Prevent users from waiting with no feedback

Use non-streaming (`exec()`) for:

- **Quick operations** - Commands that complete in seconds
- **Small output** - When output fits easily in memory
- **Post-processing** - When you need complete output before processing

## Stream command execution

Use `execStream()` to get real-time output:

```js
import { getSandbox, parseSSEStream } from "@cloudflare/sandbox";

const sandbox = getSandbox(env.Sandbox, "my-sandbox");

const stream = await sandbox.execStream("npm run build");

for await (const event of parseSSEStream(stream)) {
	switch (event.type) {
		case "stdout":
			console.log(event.data);
			break;

		case "stderr":
			console.error(event.data);
			break;

		case "complete":
			console.log("Exit code:", event.exitCode);
			break;

		case "error":
			console.error("Failed:", event.error);
			break;
	}
}
```

```plaintext
import { getSandbox, parseSSEStream, type ExecEvent } from '@cloudflare/sandbox';

const sandbox = getSandbox(env.Sandbox, 'my-sandbox');

const stream = await sandbox.execStream('npm run build');

for await (const event of parseSSEStream<ExecEvent>(stream)) {
  switch (event.type) {
    case 'stdout':
      console.log(event.data);
      break;

    case 'stderr':
      console.error(event.data);
      break;

    case 'complete':
      console.log('Exit code:', event.exitCode);
      break;

    case 'error':
      console.error('Failed:', event.error);
      break;
  }
}
```

## Stream to client

Return streaming output to users via Server-Sent Events:

```js
import { getSandbox } from "@cloudflare/sandbox";

export { Sandbox } from "@cloudflare/sandbox";

export default {
	async fetch(request, env) {
		const sandbox = getSandbox(env.Sandbox, "builder");

		const stream = await sandbox.execStream("npm run build");

		return new Response(stream, {
			headers: {
				"Content-Type": "text/event-stream",
				"Cache-Control": "no-cache",
			},
		});
	},
};
```

```plaintext
import { getSandbox } from '@cloudflare/sandbox';

export { Sandbox } from '@cloudflare/sandbox';

export default {
  async fetch(request: Request, env: Env): Promise<Response> {
    const sandbox = getSandbox(env.Sandbox, 'builder');

    const stream = await sandbox.execStream('npm run build');

    return new Response(stream, {
      headers: {
        'Content-Type': 'text/event-stream',
        'Cache-Control': 'no-cache'
      }
    });
  }
};
```

Client-side consumption:

```js
// Browser JavaScript
const eventSource = new EventSource("/build");

eventSource.addEventListener("stdout", (event) => {
	const data = JSON.parse(event.data);
	console.log(data.data);
});

eventSource.addEventListener("complete", (event) => {
	const data = JSON.parse(event.data);
	console.log("Exit code:", data.exitCode);
	eventSource.close();
});
```

```plaintext
// Browser JavaScript
const eventSource = new EventSource('/build');

eventSource.addEventListener('stdout', (event) => {
  const data = JSON.parse(event.data);
  console.log(data.data);
});

eventSource.addEventListener('complete', (event) => {
  const data = JSON.parse(event.data);
  console.log('Exit code:', data.exitCode);
  eventSource.close();
});
```

## Stream process logs

Monitor background process output:

```js
import { parseSSEStream } from "@cloudflare/sandbox";

const process = await sandbox.startProcess("node server.js");

const logStream = await sandbox.streamProcessLogs(process.id);

for await (const log of parseSSEStream(logStream)) {
	console.log(log.data);

	if (log.data.includes("Server listening")) {
		console.log("Server is ready");
		break;
	}
}
```

```plaintext
import { parseSSEStream, type LogEvent } from '@cloudflare/sandbox';

const process = await sandbox.startProcess('node server.js');

const logStream = await sandbox.streamProcessLogs(process.id);

for await (const log of parseSSEStream<LogEvent>(logStream)) {
  console.log(log.data);

  if (log.data.includes('Server listening')) {
    console.log('Server is ready');
    break;
  }
}
```

## Handle errors

Check exit codes and handle stream errors:

```js
const stream = await sandbox.execStream("npm run build");

for await (const event of parseSSEStream(stream)) {
	switch (event.type) {
		case "stdout":
			console.log(event.data);
			break;

		case "error":
			throw new Error(`Build failed: ${event.error}`);

		case "complete":
			if (event.exitCode !== 0) {
				throw new Error(`Build failed with exit code ${event.exitCode}`);
			}
			break;
	}
}
```

```plaintext
const stream = await sandbox.execStream('npm run build');

for await (const event of parseSSEStream<ExecEvent>(stream)) {
  switch (event.type) {
    case 'stdout':
      console.log(event.data);
      break;

    case 'error':
      throw new Error(`Build failed: ${event.error}`);

    case 'complete':
      if (event.exitCode !== 0) {
        throw new Error(`Build failed with exit code ${event.exitCode}`);
      }
      break;
  }
}
```

## Best practices

- **Always consume streams** - Don't let streams hang unconsumed
- **Handle all event types** - Process stdout, stderr, complete, and error events
- **Check exit codes** - Non-zero exit codes indicate failure
- **Provide feedback** - Show progress to users for long operations

## Related resources

- [Commands API reference](https://developers.cloudflare.com/sandbox/sdk/api/commands/) - Complete streaming API
- [Execute commands guide](https://developers.cloudflare.com/sandbox/sdk/guides/execute-commands/) - Command execution patterns
- [Background processes guide](https://developers.cloudflare.com/sandbox/sdk/guides/background-processes/) - Process log streaming
- [Code Interpreter guide](https://developers.cloudflare.com/sandbox/sdk/guides/code-execution/) - Stream code execution output

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