Save String to File

Sooner or later you want the workflow to write something down. A prompt log, a settings dump, a caption file for a dataset, the contents of a generated text node. ComfyUI has no built-in "write text to disk" node, and Save String to File is the gap-filler: it takes any string and writes it to a path you specify, with three behaviors for when the file already exists.

It's the output-node sibling of the pack's Load String from File - the two bookend any workflow that persists text. Write captions or config with this, read them back later with that. For batch captioning alone it's worth having: generate a prompt per image, save it as <image_name>.txt next to the image, and you've built a dataset one run at a time.

How it works

Give it a string and an absolute filepath. On execution it checks whether the target exists, then acts according to exists_behavior:

• Overwrite (default) - replace the file's contents.
• Append - add the string to the end of the existing file.
• Ignore - if the file exists, leave it completely untouched.

Parent directories are created automatically, so C:/outputs/logs/run.txt works even when logs doesn't exist yet. It writes UTF-8, and after writing it reads the file back so its output reflects what's actually on disk.

Inputs: string (the text to save), filepath (where to write), exists_behavior (the dropdown). There are no data outputs to wire - it's an output node; the file is the result.

Installing it

Save String to File is part of ComfyUI-TinyBee, a small MIT-licensed utility pack with no models to download. The easy path:

1. ComfyUI Manager → Custom Nodes Manager.
2. Search "ComfyUI-TinyBee" and install.
3. Restart ComfyUI.

Or by hand:

cd ComfyUI/custom_nodes
git clone https://github.com/TinyBeeman/ComfyUI-TinyBee

Restart and it lives under 🐝TinyBee/Util. Pure standard library under the hood - the pack's jsonata dependency only matters for its JSON Parser node.

Gotchas

The filepath is absolute, full stop. ./notes.txt resolves against ComfyUI's working directory, not your workflow, so type the whole path or compute it from a base folder. Because the node always re-runs when queued, an Overwrite workflow will happily clobber the file every run - switch to Append for a log, or Ignore if you're generating a caption only when it doesn't exist yet. And if the string input comes from a text node you've bypassed, you may get an empty file; check the wire before you blame the disk.