Preview

Preview

Preview (toolbar or F5) opens your current screen in a separate window where everything is clickable. It's the fastest way to test.

What works

• Buttons, text boxes, checkboxes, sliders, dropdowns and item lists respond, with hover and pressed feedback.
• Client actions and Client scripts run for real.
• Server actions and scripts are simulated: they appear in the console as SIMULATED SERVER…. No commands run and no Minecraft world is touched.
• Every click is logged in the console, even when nothing is assigned, so you can tell a click reached the control.

Window parts

Part	Use
Reset preview	Restores the screen's starting values.
Clear console	Empties the console.
Layout size (GUI pixels) + Apply size	Lays the screen out at another size, to test [[anchors
Console	Clicks, actions, script output (console.log) and errors with file and line.
JavaScript scratchpad + Run JavaScript	Try script code instantly against the previewed screen.

Try this in the scratchpad:

console.log('Hello from the preview!');
ui.setText('status', 'It works!');

How close is it to Minecraft?

Preview is a close approximation, not Minecraft itself:

• Layout, positions, anchors, colors, images and behavior match.
• Fonts are approximated, so exact glyph shapes differ slightly.
• Item icons are texture previews or placeholders; Minecraft draws the real models.
• Soft text shadows differ slightly.
• KubeJS scripts don't run; test them in Minecraft.

For the real thing, use the Minecraft test.

Safety

Preview scripts run in a separate, restricted process with tight time and memory limits. They can't reach your files, the network or Minecraft.