LoopStart

ComfyUI graphs are directed acyclic graphs - no cycles, ever. So when you want a chunk of a workflow to run more than once, you can't just draw the wire back on itself the way you can in Unreal blueprints. That's the whole reason this pack exists, and LoopStart is the top half of the fake.

The meshmesh-io "mm-comfyui-loopback" pack is tiny: a Loop plus a LoopStart/LoopEnd pair and a couple of image-carrying variants. LoopStart marks the top of a loop region, LoopEnd marks the bottom, and everything wired between them executes repeatedly instead of once. Think of it as the for loop you wish ComfyUI had.

The inputs that matter

There are exactly two, and honestly only one of them needs your attention.

• first_loop (true/false toggle) - this is the one that matters. It's the value the loop body starts with on pass one: wire your starting image, seed, or condition through it. On later passes the loop uses whatever LoopEnd sends back instead.
• loop (LOOP) - a marker wire. Connect it to your LoopEnd's loop input; together they define which nodes live inside the loop.

That's the node. It has no outputs - the pair communicates through the LOOP wire and LoopEnd's return value, which is why this is one of those packs that looks like a nothing node until you understand the pattern.

How to install it

ComfyUI Manager is the easy route: search "mm-comfyui-loopback", install, restart. Or the manual way:

cd ComfyUI/custom_nodes
git clone https://github.com/meshmesh-io/mm-comfyui-loopback

Then restart ComfyUI. Good news: there are no model files and no heavy dependencies - every socket in this pack is LOOP/IMAGE/boolean, so it's pure graph logic. If you loaded a shared workflow that needs it, Manager's "Install Missing Custom Nodes" will find it by name.

The honest part

This pack is old - created and last updated around two years ago - and at time of writing the GitHub repo is unreachable, so even the thin README is gone. It's effectively abandonware, and it has exactly one documented incident in the wild. It's a good one: in March 2024 this extension broke ComfyUI's node-search box. The console spat out Uncaught TypeError: ctor.title.toLowerCase is not a function because the pack was handing the frontend node titles (like LoopStart_CONDITIONING) as a list instead of a string, and the search filter died on it. The community fix was to delete the extension.

So the practical take: know it because you'll meet it in old shared workflows, and because "my node search suddenly returns nothing" is a real symptom you might have Googled past. But if you're choosing what to install today, a two-year-old abandoned loop pair isn't it - the genre never produced a clean winner, and for most loop-shaped problems you'll get further with a batch workflow or Impact Pack's iterative upscaling than with this.