String Pass Through

The docstring is one word: noop. HouStringPassThrough (display name "String Pass Through") takes a string in and hands the identical string out. Nothing is transformed, nothing is validated, nothing is stored. If you've ever wondered why someone would ship a node that does literally nothing, this is a good place to wonder - and the answer is more interesting than the node.

It's part of the Houdini ComfyUI Bridge pack, and it exists for graph plumbing reasons, not data reasons. The tell is in the input definition: str_in is declared with forceInput: True. That flag means the field can't be typed as a widget - it must be connected to a wire. So this node's real job is to force a string to exist as a connection in places where the graph needs one.

Why a string-forcing node matters

In ComfyUI, values that look like strings aren't always interchangeable. A node's text widget holds a value; a wire carries a value - and some nodes only accept one or the other. When you need a text-box value to flow along a wire into a node that insists on a connection, or you want to tap a string mid-graph without consuming it, a pass-through with forceInput is the bridge between those worlds. The Houdini bridge uses nodes like this inside its compound graphs as staging points: Houdini can promote a parameter to a node, the string has to ride a wire into the subgraph, and a dedicated pass-through keeps the handoff explicit and predictable.

There's also the cache angle. ComfyUI re-executes only what changed, working backward from output nodes. An explicit pass-through is a natural place to observe, interrupt, or force a re-run of a string's path through the graph - a placeholder node with a defined spot in the topology, rather than a wire that vanishes between two unrelated nodes.

The inputs and outputs

That's the whole interface: str_in (STRING, required, "a string") and str_out (STRING). Feed it a path, a prompt, a seed - it comes back unchanged. Nothing else to set, nothing to get wrong.

Install and context

HouStringPassThrough ships in houdini-comfyui-bridge (CapybaraCrowporation/houdini-comfyui-bridge), the community project by Rafael Drelich Valentim and Anatolii Iudanov that brings ComfyUI into Houdini - not a SideFX initiative, GPL-3.0, open-sourced late 2025 and shown at SIGGRAPH Asia 2025.

cd ComfyUI/custom_nodes
git clone https://github.com/CapybaraCrowporation/houdini-comfyui-bridge

Restart ComfyUI after cloning, or install "houdini-comfyui-bridge" via ComfyUI Manager. No dependencies, no model files - the ComfyUI half of this pack is deliberately lean; the weight lives in the Houdini plugin side (OTLs added to your Houdini userdir or HOUDINI_PATH), with the usual setup gotcha that ComfyUI Desktop's default port 8000 doesn't match the Houdini nodes' 8188.

Should you use it?

In a plain ComfyUI workflow, you almost never need a string pass-through - core Primitive nodes cover the "explicit typed value" case. Its value is inside bridge compound graphs and any hand-rolled subgraph where a string must be an explicit wire, or where you want a defined spot in the topology to intervene. It's not a debugging node and it won't show you the value. It just is - which, for a one-word-docstring node, is exactly the point.