File Name Prefix (Mikey)

ComfyUI's built-in Save Image node takes a filename_prefix string, and if you've ever noticed you can type myproject/batch1 into that field and get a subfolder for free, that's the trick this node automates. Instead of typing the date and a folder path by hand every session, FileNamePrefix builds that string for you and hands it over as a wire.

The mechanism

It's a tiny, single-purpose string builder. Feed it a few flags, get back one filename_prefix STRING output - plug that straight into the core Save Image node's filename_prefix widget (right-click it, convert to input) and you're done. Four inputs, no images involved, no side effects: this node just does string assembly.

• date (true/false, default true) - stamp today's date into the prefix.
• date_directory (true/false, default true) - nest the output under a folder named for today's date, rather than just prepending the date to the filename itself.
• custom_directory - an extra subfolder of your choosing, on top of or instead of the date folder.
• custom_text - free text appended into the prefix, good for a project name, a checkpoint name, or a short note to your future self about what this batch was testing.

Run it once per session and every save from that point lands in a dated, organized folder automatically - genuinely useful once you've got a few thousand generations piled up in one flat directory and can't find anything.

Installing

Comes bundled with the full pack, not sold separately. Through ComfyUI Manager: search "Mikey Nodes," install, restart. Or manually: cd ComfyUI/custom_nodes && git clone https://github.com/bash-j/mikey_nodes and restart. It's pure string manipulation under the hood - no models to download, no GPU dependency, nothing that can go wrong beyond a typo in a path field.

Its sibling, and the gap in the docs

There's a second node in the pack, FileNamePrefixDateDirFirst, with the exact same four inputs and the same single output. Neither node is documented by name in the pack's README - they only appear in an unexpanded "Additional Nodes" bullet list. Going by the name alone, the difference is almost certainly folder ordering: whether the date directory or your custom directory comes first in the resulting path. I can't confirm the precise ordering logic without reading the node's source, so if the exact folder nesting matters to your pipeline, drop both nodes on a test canvas and compare the string each one outputs before you commit to one.

Troubleshooting

• Nothing changes when you edit the widgets. Make sure you actually converted Save Image's filename_prefix widget to an input and wired this node's output into it - if you left it as a plain text widget, FileNamePrefix's output goes nowhere.
• Forward slashes vs backslashes. If you're typing a custom_directory value by hand, use forward slashes (/) regardless of OS - that's the convention ComfyUI's own path handling expects, and it avoids the classic Windows-path-in-a-string-field bug.
• Can't find the node after install. This is the standard "missing custom node" ComfyUI complaint - restart the whole ComfyUI process (not just refresh the browser tab) after installing any new pack, and check ComfyUI Manager's log for install errors if it still doesn't show up.