Preview Boolean

Booleans are the most invisible values in ComfyUI. An on/off flag flies out of some node, into a switch or a condition, and you have no idea whether it's true or false until the downstream behavior surprises you. Preview Boolean is the two-second fix: a dead-end display node that shows the actual boolean on the canvas.

It's from ComfyUI Extended, the small dependency-free utility pack, and it's the boolean twin of the pack's Preview Text / Preview Float / Preview Integer nodes. Genuinely useful when you're building conditional workflows and half the battle is just knowing what the condition was.

How it works

The node takes one required input, boolean (BOOLEAN), marked forceInput in the source - wire something in rather than expecting to type a value. On execution it sends the value over a websocket to the browser, and the pack's frontend (web/preview.js) writes it into a read-only widget on the node. True becomes true, false becomes false, lowercase.

It's an output node (OUTPUT_NODE = True) with no output sockets. It's the end of a wire, deliberately. That's the whole mechanism - one websocket push, one read-only widget, no files, no dependencies.

Install

Same as the rest of the pack, which needs nothing beyond ComfyUI itself:

cd /path/to/your/ComfyUI/custom_nodes
git clone https://github.com/rookiepsi/comfyui-extended.git

Restart, and it's under comfyui-extended/preview in the node menu. Or use ComfyUI Manager and search "ComfyUI Extended". No models, no pip installs.

Common issues

• Shows nothing until you run. The value is pushed after execution. Run the queue.
• Stale/blank widget after an update. Hard-refresh the browser so the pack's web/ JS reloads.
• You can't type into it. forceInput means it wants a wired connection, which is the point - it's a probe, not a toggle.

The honest take: it's a one-trick node, and the trick is small. But when you're debugging a switch that's flipping the wrong way, seeing false printed on the canvas beats three guesses and a restart.