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Kernel’s browsers support running with custom Chrome extensions. Chrome extensions must be unpacked and can be uploaded to Kernel via the CLI or API.

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Uploading extensions

Here is a simple example of an unpacked extension: 
document.body.innerHTML = document.body.innerHTML.replace(/AI/g, "A1");
Once these files are in place, you can upload them to Kernel via the CLI (or API): 
kernel extensions upload ./my-extension --name my-extension
Extensions uploaded to Kernel are assigned a random ID, but you can also give them a name for easier reference. This name must be unique within your organization.

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Using extensions in a browser

Passing the extension name or ID to the create method will load it into the browser: 
import { Kernel } from '@onkernel/sdk';

const kernel = new Kernel();
const kernelBrowser = await kernel.browsers.create({
    extensions: [{ name: "my-extension" }],
});

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Using extensions directly from the Chrome Web Store

Kernel’s CLI offers a command for fetching and unpacking extensions directly from the Chrome Web Store. Simply pass the URL of the extension you want to download and the CLI will download the extension and unpack it into the specified directory.
CLI
kernel extensions download-web-store https://chromewebstore.google.com/detail/shutterfly-address-book-e/lddlpciejomhjehckimopnomegilaocb --to ./downloaded-extension
From here you can upload the extension to Kernel as normal.
CLI
kernel extensions upload ./downloaded-extension --name my-extension

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Loading an extension into a running browser

If you have a browser running and would like to load an extension into it after the browser session has started, Kernel also allows you to do that via the CLI (or API):
CLI
kernel browsers extensions upload <session_id> ./my-extension
Note that this will restart the browser process and break any connections to the browser CDP URL.

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Extensions requiring enterprise policies

For a complete list of available extension settings and policies, refer to the Chrome Enterprise Policy documentation.

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Uploading extensions requiring enterprise policies

Some Chrome extensions require elevated permissions that Chrome will only grant when the extension is installed via enterprise policies. These extensions cannot be loaded with the standard --load-extension flag and require special handling.

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What are enterprise policy extensions?

Extensions that require enterprise policies typically:
  • Use permissions like webRequestBlocking or webRequest with blocking capabilities
  • Need to intercept and modify network requests before they’re sent
  • Require installation via Chrome’s ExtensionInstallForcelist policy
Common examples include extensions for network filtering, request signing, or advanced content modification.

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Required files for upload

When uploading an extension that requires enterprise policies to Kernel, your extension directory or zip file must include:
  1. Extension source files - Your manifest.json and all extension code (background scripts, content scripts, etc.)
  2. update.xml - A Chrome update manifest that points to the .crx file location
  3. .crx file - The signed and packed extension file
The .crx file and update.xml are required for Kernel to serve the extension via Chrome’s ExtensionInstallForcelist policy. If you’re deploying extensions from the Chrome Web Store via ExtensionInstallForcelist, these files are optional since Chrome uses the Web Store’s default update URL.

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Automatic detection and validation

Kernel automatically detects extensions that require enterprise policies by analyzing the manifest.json file during upload. No manual configuration is needed. Detection process:
  1. You upload an extension via CLI or API
  2. Kernel scans the manifest.json for permissions like webRequestBlocking
  3. If enterprise policies are required, Kernel validates the required files are present

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How it works

Once you successfully upload an enterprise policy extension, Kernel handles the rest automatically:
  1. Upload - You upload your extension with all required files
  2. Detection - Kernel detects the enterprise policy requirement from the manifest
  3. Policy configuration - Extension is automatically added to ExtensionInstallForcelist
  4. File serving - The kernel-images server serves update files at http://127.0.0.1:10001/extensions/{extension-id}/update.xml
  5. Installation - Chrome installs the extension via enterprise policy when the browser starts
No additional HTTP server or manual policy configuration is needed. The extension works seamlessly in any browser session that it’s uploaded to.