Step Preview 🆎

You queue a 25-step render, and by step four the picture is already wrong - head cropped, extra arm, the pose nowhere near what you asked for. Without a preview you get to find that out two minutes later, then change the seed and do it again. Step Preview 🆎 shows the picture forming inside a node on your canvas and puts a STOP button next to it. That's the whole pitch, and it's a good one.

What it actually is

A monitor, not a step in the pipeline. Drop it anywhere - it takes no wires, and it shows whatever sampler in the workflow is currently drawing. The caption says how far along the run is ("step 3 of 8"); when the run finishes, the saved picture replaces the blurry last step and stays until the next run. The word at the right of the bar reads running, done, stopped or failed.

Same category as the quality-of-life packs you install first: no generation capability, it just makes a graph bearable to work in. You install it because waiting blind is the worst part of iterating.

Why the node has no inputs and no outputs

The schema for AUSBOSS_NODES_StepPreview is empty on both sides, and that's how it ships: INPUT_TYPES returns nothing, RETURN_TYPES is an empty tuple, and the noop function is never called. The source says so in a comment - with no outputs, ComfyUI never executes the node. It can't force your graph to run, and it can't echo anything downstream.

So what does it do? Two halves:

The server half is a hook. The pack registers a handler on ComfyUI's prompt server, and each time a prompt is queued it checks whether that prompt contains this node (or a Save Image / Save Video with its steps switch on). If it does, and nobody else chose a preview method, it sets extra_data.preview_method = "auto" for that run. That's why it needs no wires - it piggybacks on the queue request, not on data flow. Fresh installs ship with previews off, so without this you'd see nothing.

The browser half is the panel: it listens for ComfyUI's per-step preview and progress events, paints the newest picture into the node, and wires the buttons to ComfyUI's interrupt and queue-clear calls. auto means a TAESD from models/vae_approx if you have one, otherwise a fast latent-to-RGB colour guess, capped at 512 px on the long side.

It never overrides a preview method you picked, in Settings or with --preview-method on the command line, and runs queued from another workflow tab aren't shown here.

The controls that matter

There are only two buttons and no parameters to set.

STOP interrupts the current run. Nothing after the sampler executes, which means nothing gets saved - a stopped run leaves the last step it reached on the node, and the next item in the queue still starts. STOP ALL · N only shows when runs are waiting; it empties the queue and then interrupts, so a 20-image batch can die after picture two. Want the finished file? Let it run - previews land in temp/, saves land in output/.

Install

ComfyUI-Manager → Custom Nodes Manager → search AusBoss, or from the command line:

cd ComfyUI/custom_nodes
git clone https://github.com/ausboss/ComfyUI-AusBoss.git

comfy node install ausboss-nodes does the same via the registry. Restart and search the node library for AusBoss. Nothing else to install: pyproject.toml declares no dependencies, the node uses the Pillow, NumPy, Torch and PyAV already in ComfyUI, and there are no weights. Optionally drop a TAESD file in ComfyUI/models/vae_approx/ so the steps are sharp enough to judge detail, not just layout.

Where people get burned

Nothing ever appears. Check the Live preview method in Settings first. If you once set it to none, that counts as a choice the pack will not override, and you get a permanently empty node. Put it back to default (or auto).

It's a blurry mess of blocks. That's latent2rgb doing its best. Install a TAESD and ComfyUI will use the real decoder instead.

Some models show nothing at all. The help doc calls out SeedVR2: no TAESD exists for it and latent2rgb doesn't apply. Nothing to fix.

STOP feels ignored. ComfyUI checks for an interrupt at step boundaries, so a slow step, a VAE decode, or the second half of a hires pass has to finish before the button lands. People hit the same lag on the interrupt button itself, and on a long step it can feel like a minute.

It does nothing on its own. Because it never executes, a graph whose only "outputs" are this node will simply not run. Keep a Save Image or Preview Image in the workflow - this is a window onto a run, not a reason to have one.

And if a blurry preview is all you wanted, set the Live preview method in Settings and skip the pack. The reasons to install it are the STOP button and a view big enough to read.