📅 Rennart Date String

Rennart Date String is the smallest node in the ComfyUI-Rennart pack, and it does exactly one thing: output the current date and time as a string. You give it a format string in Python's strftime syntax and it hands you date_string. That's the entire contract. It's a pure plumbing node in the sense the ComfyUI ecosystem uses the word - it touches no pixels, generates nothing, and exists to feed other nodes a value.

What you'd use it for

Honestly? Mostly filenames and bookkeeping. The classic use is wiring it into a text input for a filename template or a Save Image-style node so every run stamps the output with the date. Combine it with a workflow-level text concatenation and you get render_2026-08-30 instead of a folder full of ComfyUI_00042_. It also earns its keep as a timestamp for log/note nodes, or as a way to prove to yourself which run generated what when you're comparing outputs side by side.

How it works

Under the hood it's a single datetime.now().strftime(format) call, and the key detail is in how it behaves over time: the node overrides IS_CHANGED to return the current Unix timestamp, which tells ComfyUI's cache the result is stale on every run. That means it always fires - you get a fresh time every single execution, not a cached value from the first run. This is the documented "always rerun" trick from ComfyUI's plumbing layer, and here it's exactly right, because a timestamp that doesn't update would be worse than useless.

The input that matters

Just one: format, defaulting to %Y-%m-%d (which gives you 2026-08-30). Use standard strftime codes:

• %Y-%m-%d → 2026-08-30
• %Y%m%d_%H%M%S → 20260830_153045
• %A, %B %d → Sunday, August 30

Keep in mind the output uses whatever your machine's local timezone is set to. If you run a batch overnight and expect filenames grouped by UTC day, you'll need to adjust - the node has no timezone input, it just reads the system clock.

Install and gotchas

It ships with the ComfyUI-Rennart pack:

# ComfyUI Manager: search "ComfyUI-Rennart", or:
cd ComfyUI/custom_nodes
git clone https://github.com/Rennart2025/ComfyUI-Rennart

Restart ComfyUI; the node lives under Rennart/Utils. No models, no extra dependencies beyond what ComfyUI already has.

One honest gotcha: because the node is always dirty (that IS_CHANGED timestamp), anything downstream of it reruns every time too. That's normally what you want with a date node, but if you chain it into something expensive and don't actually need the live value, you're paying for re-execution you didn't ask for. The "always rerun" behavior is a feature for a clock and a cost for whatever it feeds - plan the graph accordingly.