MF Save Data (json/csv/xml/yaml)

ComfyUI's "Save Image" is great at pixels and useless at everything else. When you want to persist a prompt, a config, an API response, or an LLM's output to disk, MF Save Data (json/csv/xml/yaml) (MF_SaveData) is the writer half of MF PipoNodes' data pair - take any string, pick a format, and write a real file. From the MF PipoNodes pack (pierreb-mf / Moment Factory).

How it works

Four required inputs, all of which you'll set:

• data - the string to save (marked as a forced input, so it takes a wire rather than hand-typing).
• output_path - the directory, default "output" (relative to ComfyUI's working directory, so usually ComfyUI/output). It's created automatically if missing.
• filename - base name without extension, default "data".
• format - enum: json, xml, csv, yaml.

One output: filepath (STRING) - the full path of the file you just wrote.

The format handling is "try to be smart, degrade gracefully":

• JSON - parses your string and re-dumps it pretty-printed; if it isn't valid JSON, writes it as-is.
• CSV - if your data parses as a list of objects, writes header + rows; otherwise writes the whole string as one cell.
• XML - parses and pretty-prints, or wraps the raw text in a <data> element.
• YAML - parses as JSON first, then dumps to YAML; needs pyyaml (it's in the pack's requirements).

There's one genuinely useful nicety: the node strips markdown code fences from the input before writing. So when an LLM returns ```json ... ```, the fences vanish and you get a valid file. That alone saves a regex node.

The pattern it exists for

The obvious one: an LLM node outputs a JSON string, and you want it on disk as actual JSON for another tool.

LLM node ──▶ MF Save Data (format: json) ──▶ filepath ──▶ log it or display it

Pair it with MF Read Data for the full persist-and-reload loop: save settings at the end of a run, load them back at the start of the next. And it's the natural audit trail complement to MF Save Log File when you want structured output instead of a timestamped text file.

Install

cd ComfyUI/custom_nodes/
git clone https://github.com/pierreb-mf/ComfyUI-MF-PipoNodes
cd ComfyUI-MF-PipoNodes
pip install -r requirements.txt

Restart after, or ComfyUI Manager → "MF PipoNodes". Only aiohttp and pyyaml are pulled in.

Gotchas

• Relative output_path is relative to the ComfyUI process, not to the pack or your home. "output" lands in ComfyUI/output, which is almost always what you want - just don't assume absolute paths.
• "Smart" parsing can surprise you. Feed valid JSON into format: json and it gets re-serialized (that's fine). Feed almost-valid JSON and the fallback writes it verbatim, so the file may still be invalid when another tool opens it.
• Errors come back through filepath - on failure the output is a string like "Error: ...", so check it before wiring it into a path.