Viewports

Kernel browsers allow you to configure the viewport size and refresh rate when creating a browser session. The viewport configuration determines the initial browser window dimensions and display refresh rate. The refresh rate can be explicitly specified or automatically determined based on the width and height if they match a supported configuration.

Default viewport

If the viewport parameter is omitted when creating a browser, the default configuration is 1920x1080 at 25Hz.

// Uses default viewport (1920x1080@25Hz)
const defaultViewport = await kernel.browsers.create();

Setting viewport configuration

You can configure the viewport when creating a browser by specifying the viewport parameter with width and height. The refresh_rate is optional and will be automatically determined from the dimensions if they match a supported configuration:

import Kernel from '@onkernel/sdk';

const kernel = new Kernel();

// Explicitly specify refresh rate
const kernelBrowser = await kernel.browsers.create({
  viewport: {
    width: 1920,
    height: 1080,
    refresh_rate: 25
  }
});

// Auto-determine refresh rate from dimensions (25Hz for 1920x1080)
const kernelBrowserAuto = await kernel.browsers.create({
  viewport: {
    width: 1920,
    height: 1080
  }
});

Supported viewport configurations

Kernel supports specific viewport configurations tuned for optimal performance and Computer Use compatibility. When you provide width and height without specifying refresh_rate, it will be automatically determined if the dimensions match one of the supported resolutions exactly. The following resolutions are supported:

When specifying a viewport:

• Width and Height are required
• Viewport configurations outside of the supported list are available, but they are provided on a "use at your own risk" basis and may not work as expected.
• Refresh Rate is optional - if omitted, it will be automatically determined from the width and height combination

Example configurations

// Full HD (1920x1080) at 25Hz - explicit refresh rate
const fullHD = await kernel.browsers.create({
  viewport: {
    width: 1920,
    height: 1080,
    refresh_rate: 25
  }
});

// Full HD (1920x1080) - auto-determined 25Hz (Default configuration)
const fullHDAuto = await kernel.browsers.create({
  viewport: {
    width: 1920,
    height: 1080
  }
});

// QHD (2560x1440) - auto-determined 10Hz
// Note: May affect live view responsiveness
const qhd = await kernel.browsers.create({
  viewport: {
    width: 2560,
    height: 1440
  }
});

// XGA (1024x768) - auto-determined 60Hz
const xga = await kernel.browsers.create({
  viewport: {
    width: 1024,
    height: 768
  }
});

// WUXGA (1920x1200) at 25Hz - explicit refresh rate
const wuxga = await kernel.browsers.create({
  viewport: {
    width: 1920,
    height: 1200,
    refresh_rate: 25
  }
});

Dynamically changing the viewport

You can change the viewport of a browser after it has been created using the update browser endpoint.

// Create a browser with default viewport
const kernelBrowser = await kernel.browsers.create();

// Later, change the viewport
await kernel.browsers.update(kernelBrowser.session_id, {
  viewport: {
    width: 1024,
    height: 768
  }
});

Force resizing during recording

If you need to resize the viewport while a replay is actively recording, set force to true in the update request. This stops the current recording, resizes the viewport, and restarts the recording — resulting in multiple replay segments for the session.

await kernel.browsers.update(kernelBrowser.session_id, {
  viewport: {
    width: 1024,
    height: 768,
    force: true
  }
});

Considerations

• The viewport configuration is set when the browser is created and applies to the initial browser window
• Higher resolutions (like 2560x1440) may impact the performance and responsiveness of live view sessions
• The viewport size affects how websites render, especially those with responsive designs
• Screenshots taken from the browser will match the configured viewport dimensions