Log (STRING)

Debugging text in ComfyUI is a pain. A string leaves one node, passes through a concatenate or a replace, and you have no idea what it actually looks like when it reaches the CLIP encoder. Log (STRING) is the node you drop into that gap: it prints the value to the console and hands it straight through, so you can see what's really in your prompt without breaking the wire.

The class name is LogString and it's part of RF Nodes, a small pack built around manipulating primitives - numbers, text, booleans. This is the text-flavored member of a whole family of Log nodes (LogInt, LogFloat, LogBool, and friends), and it's the one you'll reach for when the prompt you built from pieces isn't coming out the way you expected.

How it works

It's gloriously simple: LogToConsole(prefix, value) prints a line to the terminal you launched ComfyUI from - in cyan, with your prefix - and then the node returns the value unchanged. Because it passes the string through, you can splice it into the middle of a chain: wire your dynamic text in, wire the output on to the next node, and watch what goes by.

The passthrough matters more than it sounds. It means the Log node is never a dead end; it's an inline tap, not a sink.

The inputs that matter

• value - the string to log. Note the forceInput flag in the schema: this input must be wired, you can't just type into it. That's deliberate - the node's job is to observe a value in flight.
• prefix - a label printed before the value (default Value:). This is your main debugging tool. Give each Log node a distinct prefix (NEG:, filename:, lora:) and you can grep the console for exactly the line you care about instead of squinting at a wall of cyan.

Output: STRING - the same value you fed in, unmodified. Wire it onward as if the node wasn't there.

Installing RF Nodes

The pack has no dependencies and no model downloads - just Python's standard library. Install through ComfyUI Manager (search "RF Nodes"), or manually:

cd ComfyUI/custom_nodes
git clone https://github.com/foxtrot-roger/comfyui-rf-nodes

Restart ComfyUI and you'll find the Log nodes under RF in the menu.

Common issues

• "The node does nothing." - It does something; it's just not happening where you're looking. The log line goes to the terminal/console where ComfyUI is running, not the browser. If you launched ComfyUI from a desktop shortcut, you may not even see it - run ComfyUI from a terminal and watch that window.
• "Too many log lines, can't tell them apart." - Set a distinctive prefix on each. That's the whole design.
• The value gets printed once per run but it's the same every time. That's normal - logging a constant string logs a constant. If you want to see variation, log something that changes (a timestamp, a seed-driven value).