---
description: Handle real-time output from commands and processes.
title: Stream output
image: https://developers.cloudflare.com/og-docs.png
---

[Skip to content](#main-content)

> Documentation Index  
> Fetch the complete documentation index at: https://developers.cloudflare.com/sandbox/llms.txt  
> Use this file to discover all available pages before exploring further.

# Stream output

Last updated Aug 24, 2026|Copy as Markdown|[View as Markdown](https://docs-durable-objects-instance-replaced-errors.previews.developers.cloudflare.com/sandbox/guides/streaming-output/index.md)|[Agent setup](https://docs-durable-objects-instance-replaced-errors.previews.developers.cloudflare.com/agent-setup/)

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

Coming soon: Sandbox SDK 1.0

This page documents streaming helpers on today's stable `@cloudflare/sandbox` package.

In the **1.0 preview** (`@next`), stream with process handle methods such as `logs()` after `exec(argv)`. Refer to [Process execution](https://docs-durable-objects-instance-replaced-errors.previews.developers.cloudflare.com/sandbox/1-0-preview/processes/) or the [Processes API](https://docs-durable-objects-instance-replaced-errors.previews.developers.cloudflare.com/sandbox/1-0-preview/api/processes/).

## 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://docs-durable-objects-instance-replaced-errors.previews.developers.cloudflare.com/sandbox/api/commands/) \- Complete streaming API
* [Execute commands guide](https://docs-durable-objects-instance-replaced-errors.previews.developers.cloudflare.com/sandbox/guides/execute-commands/) \- Command execution patterns
* [Background processes guide](https://docs-durable-objects-instance-replaced-errors.previews.developers.cloudflare.com/sandbox/guides/background-processes/) \- Process log streaming
* [Code Interpreter guide](https://docs-durable-objects-instance-replaced-errors.previews.developers.cloudflare.com/sandbox/guides/code-execution/) \- Stream code execution output

Was this helpful?

YesNo

## On this page

[![](https://docs-durable-objects-instance-replaced-errors.previews.developers.cloudflare.com/_astro/logo.te5VL_aD.svg)Docs](https://docs-durable-objects-instance-replaced-errors.previews.developers.cloudflare.com/)

```json
{"@context":"https://schema.org","@type":"TechArticle","@id":"https://developers.cloudflare.com/sandbox/guides/streaming-output/#page","headline":"Stream output · Cloudflare Sandbox SDK docs","description":"Handle real-time output from commands and processes.","url":"https://developers.cloudflare.com/sandbox/guides/streaming-output/","inLanguage":"en","image":"https://developers.cloudflare.com/og-docs.png","dateModified":"2026-08-24","publisher":{"@type":"Organization","name":"Cloudflare","description":"One platform for your apps, agents, and workforce. Build, secure, and scale without managing infrastructure","url":"https://www.cloudflare.com/","sameAs":["https://github.com/cloudflare","https://www.linkedin.com/company/cloudflare","https://x.com/cloudflare"],"logo":{"@type":"ImageObject","url":"https://developers.cloudflare.com/logo.svg"},"address":{"@type":"PostalAddress","streetAddress":"101 Townsend St","addressLocality":"San Francisco","addressRegion":"CA","postalCode":"94107","addressCountry":"US"},"contactPoint":[{"@type":"ContactPoint","contactType":"Customer Support","url":"https://support.cloudflare.com/","availableLanguage":["English"]},{"@type":"ContactPoint","contactType":"Sales","url":"https://www.cloudflare.com/contact/","availableLanguage":["English"]}]},"isPartOf":{"@type":"WebSite","@id":"https://developers.cloudflare.com/#website","name":"Cloudflare Docs","url":"https://developers.cloudflare.com/"}}
```