Debug (mtb)

Every ComfyUI graph eventually hits the point where something isn't the value you expected and there's no obvious way to look at it mid-pipeline. Debug is MTB Nodes' answer: a node you can wire into basically any connection to inspect what's actually there, without breaking the rest of the graph.

How it works

Straight from the node's own description, it "tries to provide information about any input types supported by Comfy," using the same dynamic-inputs mechanism a few other mtb nodes share - wire something in and the node grows a slot for it, rather than declaring a fixed, typed socket up front. It specifically handles a handful of common types with real detail and falls back to a plain string representation for anything it doesn't recognize, so it never just errors out on an unfamiliar type - worst case, you get a generic repr instead of a structured view.

The inputs that matter

• output_to_console (default false) - mirrors whatever the node displays into ComfyUI's actual terminal/console log, not just the on-node display. Turn this on if you're running headless or through the API, where there's no graph UI open to look at the node's own output panel.
• as_detailed_types (optional, default false) - asks for a more verbose breakdown of the type information rather than a compact summary. Flip this on when a short summary isn't enough to tell you what's wrong - a tensor's shape and dtype instead of just "IMAGE," for instance.

It's an output node (is_output_node: true) with no data outputs - it's a sink for inspection, meant to be a dead-end branch off whatever you're checking, not something you keep building on.

Installing it

ComfyUI Manager: search MTB Nodes, install, restart. Manually:

cd ComfyUI/custom_nodes
git clone https://github.com/melMass/comfy_mtb

then restart ComfyUI. No models, no heavy dependencies - it's introspection, not inference.

Common issues

The main thing people miss is that this node doesn't feed back into your graph - it's a terminal branch. If you want to see a value and also keep using it further downstream, wire the same output to both Debug and whatever consumes it next; don't expect Debug to pass anything through.

output_to_console is easy to forget about when running via the API or in a headless/queue setup - without it, the debug output only ever shows up on the node itself in the graph UI, which does you no good if nothing's rendering that UI. Turn it on any time you're debugging a workflow that isn't running interactively.

And the pack-wide behavior that applies here as much as anywhere: MTB logs [comfy_mtb] Some nodes (N) could not be loaded at startup instead of crashing outright when one node fails to import, with a pointer to http://127.0.0.1:8188/mtb for the real cause - a real, confirmed pattern from other users' install logs. If Debug doesn't show up after installing, check that line first.