StepFun String Combiner

StepFun String Combiner is a plain local utility wearing StepFun branding. Despite the name and the pack it ships in, it doesn't call any API, doesn't need a key, and doesn't touch the cloud. It takes up to three text inputs, drops the empty ones, and joins the rest with commas - then hands you both the joined string and the individual strings as a list. If you've used the pack's own role2story example workflow, you've seen it working behind the scenes, stitching pieces of prompts together so a cloud node gets one tidy string.

Why would you want this? Because the moment you chain vision-model outputs into prompt-generation steps, you end up with strings scattered across nodes, and you need one deterministic way to merge them. The combiner is that way. It's the glue that turns "a caption from one node" plus "a style tag from another" into a single prompt line.

How it works

Nothing clever. Each input is stripped of surrounding whitespace, inputs that are empty after stripping are discarded, and the survivors are joined with ,. That's the whole mechanism - which is why it's a nice, boring, predictable node to build workflows around.

Inputs and outputs

• input_1, input_2, input_3 - three required multiline string fields. All three are marked required, but empty ones simply get skipped, so you can leave one or two blank without an error.
• string_array - the non-empty inputs as a list (STRING_LIST). Wire this into a node that accepts a string list.
• combined_string - the same strings joined with commas, as a plain string. This is the one you'll reach for 90% of the time, since most downstream nodes want a single string.

One thing to keep straight: the join is plain concatenation, not CSV. If your inputs contain commas of their own, the result gets messier rather than smarter. And because empties are dropped, a node with two empty inputs and one filled one returns just that one string - which is usually what you want, but it means the combiner can't be used to detect "no input" downstream.

Installing

It ships in the StepFun pack, so installation is the pack's installation:

cd ComfyUI/custom_nodes
git clone https://github.com/chenbaiyujason/ComfyUI_StepFun
cd ComfyUI_StepFun
pip install -r requirements.txt

Or search "ComfyUI-SCStepFun" in ComfyUI Manager. Restart, and it'll be under the StepFun category alongside the API nodes. You do not need an API key to use this one.

Troubleshooting

There isn't much to go wrong. If the node shows red, check that you're not feeding it a non-string type - the inputs are strict strings, so a list or image output won't connect. If your combined output looks wrong, it's almost always a stray comma or whitespace in one of the inputs, not a node bug.

Honest take: this is a utility node that would be equally at home in a general-purpose pack like WAS or rgthree, and there are a hundred functionally identical string mergers out there. Use it because you're already installing this pack for the chat nodes - not as a reason to install the pack in the first place.