🐟String Formatter

🐟String Formatter gives you real Python f-string formatting in the graph - not the fixed placeholder replacements most ComfyUI text nodes offer, but the whole syntax: number padding, string width, dict formatting, conditional expressions if you want to get silly. If you've ever wanted to build a prompt like "{arg1} in the style of {arg2}, {arg3:>20}" and have it actually respect the format spec, this is the node.

How it works

One required input, template, a multiline string written in f-string syntax. Then arg1 through arg10 - ten optional inputs that accept any type (*), so you can plug in strings, numbers, lists, dicts, whatever. Your template references them as {arg1}, {arg2}, and so on, and the node assembles the final string.

template: "你好 {arg1}，欢迎来到 {arg2}！"
arg1: 小明    arg2: ComfyUI
→ "你好 小明，欢迎来到 ComfyUI！"

Numbers, dicts, and lists all format naturally - {arg1} with a dict input prints the dict's repr, which makes it handy for injecting structured metadata into a prompt. The output is formatted_string, and the node also displays it on the graph (there's a small JS extension that renders the result in a read-only widget), which is a nice touch for prompt work.

Two things the README gets wrong

The README claims unprovided arguments are "ignored" and that referencing one gives a Format Error. Tested against the actual code: an unprovided arg defaults to None, and {arg2} formats as the literal text None in your output. So a template with a missing arg silently prints "None" into your prompt - keep an eye on that, because it's exactly the kind of quiet corruption you'll blame on the model.

Second: the template is evaluated with Python's eval. That's what buys you full f-string syntax, and it's also the thing to respect. Builtins are reachable - your template could in principle call __import__('os') and run arbitrary code. That's fine for your own workflows (it's your machine, your templates), but don't paste a template you don't trust from a stranger's workflow. Treat templates as code.

Error handling

If the template fails - a typo'd variable, an unterminated format spec - you get a Format Error: <message> string on the output instead of a crash, plus the result shown on the node. It's forgiving enough to debug live, but remember the None behavior above; not every problem announces itself.

Installing

ComfyUI Manager, search "ComfyUI-String-Helper", install, restart. Or:

cd ComfyUI/custom_nodes
git clone https://github.com/liuqianhonga/ComfyUI-String-Helper.git

The pack ships translators and chardet as dependencies, but this node is pure stdlib - no translation, no models, no network.

Where it fits

Use it anywhere you'd use the built-in Text Concatenate but need real formatting - numbers padded for filenames, dates spliced into prompts, model metadata folded into a text string that feeds a CLIP encoder. For the heavy lifting on dynamic prompt assembly, pair it with StringMatcher (conditional value picking) and StringConverter (typed output), and you've got a mini templating engine with no external services.