😺NKD Popup Preview

ComfyUI's built-in preview is an inline thumbnail on the canvas. Fine for checking a result - genuinely annoying when you're iterating on a big workflow and want the output on the other screen, blown up, while you keep editing. NKD Popup Preview is the node that floats your generated image in a separate window you can drag onto a second monitor and maximize. It does exactly one thing, and it's hard to find fault with that.

It's as simple as a node gets: one image input (any IMAGE), no outputs, an output node you hang at the end of the graph. Wire a VAE Decode into it, queue, and a popup window opens showing the current output, refreshing live as each result lands. The whole thing is driven from the pack's JavaScript - window.open on a viewer page, or Picture-in-Picture where your browser supports it. Drag the popup to monitor two, hit maximize, and suddenly you have a proper "render screen" without alt-tabbing to fullscreen every five minutes.

The genuinely clever bit is the "primary" state. The README frames it plainly: you can have multiple popup previews in one workflow, mark one as primary, and then trigger or refresh just that one. The author's own pitch (they posted the pack on r/comfyui) is that this lets you queue only what you're actually previewing - when you're tuning LoRA concept sliders or nudging a weight and re-running constantly, the primary node has a shortcut (Shift+Q) to re-run just that output. No scrolling back from the middle of nowhere to find the preview node, and you're not paying for a full graph re-run each tweak. For anyone doing long, fiddly adjustment sessions, that's the feature that makes this more than a toy.

You can also pair it with the pack's NKD Reference node: hold Space (or the Hold for Ref button) to flash a reference image over the current output, which turns the same popup into an A/B compare tool. That's covered on the reference node's own page, but it's worth knowing the two are designed to work together.

Install

Zero friction here: no Python dependencies (the pyproject declares none), no model files, nothing to download. Either run

cd ComfyUI/custom_nodes
git clone https://github.com/Nekodificador/ComfyUI-NKD-Preview-Tools.git
# restart ComfyUI

or search "NKD Preview Tools" in ComfyUI Manager. The repo was originally ComfyUI-NKD-Popup-Preview - this page's URL - and that old name still redirects fine.

Common issues

The one real failure mode is your browser, not the node. The popup is opened with window.open, so the popup blocker will happily kill it on first use. If nothing appears, look at the address bar and allow pop-ups for your ComfyUI host (localhost or wherever you run it). Second gotcha, straight from the source: the JavaScript itself notes that Electron blocks window.open - so if you're running ComfyUI inside an Electron-style wrapper, the popout won't open. Use a real browser (Chrome, Firefox, Edge) and it works. Beyond that, the node is unambitious and reliable - which, given how often preview nodes in this ecosystem try to be everything at once, is almost a compliment.