join (from LIST)

You've built a list of strings - prompt segments, tags, filenames, values pulled out of a file - and now you need them as one string with something between them. That's join (from LIST). It takes a Python LIST of strings plus a separator and concatenates them: sep goes between elements, never at the start or end.

The most obvious use is assembling prompts from parts: a list of tags joined with commas, or a list of prompt phrases joined with spaces to feed a text encoder. It's also how you turn a list of filenames into a single comma-separated value to pass somewhere that wants one string.

How it works

Under the hood it's Python's sep.join(strings), and that's worth knowing because the semantics are exact. ["a", "b", "c"] with sep=", " gives "a, b, c" - the separator is inserted between elements only. No leading or trailing separator. And empty elements are honored: ["a", "", "c"] with sep="," gives "a,,c". Nothing is dropped or cleaned for you.

One naming trap to flag: this is the from LIST variant, which takes a Python LIST as a single variable. The pack also has a StringDataListJoin that takes a native ComfyUI data list and is wired to process items as a batch. Don't grab the wrong one - if your source is a data list, use the data-list join; if it's a LIST variable, this is your node.

Inputs and outputs

Two required inputs:

• strings - a LIST of strings. This is the thing you're joining.
• sep - the separator, a STRING that defaults to " " (a single space).

Output is one STRING: the concatenated result. That wires straight into any text input - a prompt field, a filename builder, another string node.

Installing it

Ships in the Basic data handling pack by StableLlama. ComfyUI Manager: search "Basic data handling", install, restart. Manual route:

cd ComfyUI/custom_nodes
git clone https://github.com/StableLlama/ComfyUI-basic_data_handling

The pack is pure Python - zero dependencies, no model downloads - which makes it a fixture in shared workflows that want string handling without an install saga. Under Basic/STRING in the menu.

Common issues

The separator default is a space, and people expect a comma. If you're building CSV or comma-separated values, set sep to "," explicitly - the default is just "put a space between things", which is right for joining words and wrong for joining data. The other classic: an empty string in your list produces doubled separators ("a,,c"). If your list comes from a split and you don't want empties, filter it first with the pack's filter nodes. And watch the LIST-vs-data-list distinction - connecting a data list here works visually but behaves differently than you expect, because a data list is a batch of individual values and a LIST is one variable holding many.