startswith

Conditional workflows are where ComfyUI stops being a paint-by-numbers image tool and starts being a real program, and startswith is a genuine gate for them. It answers one binary question - does this string begin with that? - and hands you a BOOLEAN you can feed straight into the pack's if/else or flow-select nodes. Filename prefix, model name, tag start - if you need to branch on it, this is the check.

How it works

Straight pass-through to Python's str.startswith(), wrapped in the Basic data handling pack (StableLlama, zero runtime dependencies). Two required inputs: string (what you're testing) and prefix (what you're checking for). Both are plain STRINGs.

There are two optional INT inputs if you only care about part of the string: start (default 0, where to begin the check) and end (default 0). The end default is the sneaky one - an end of 0 is treated as "to the end of the string," so you can safely ignore it for whole-string checks. Set start to, say, 7 and the node only looks at characters from position 7 onward.

The output is BOOLEAN - True or False. That's it. It's a pure predicate; it doesn't extract anything.

The workflow pattern

This node is half of a pattern, not the whole thing. The classic graph:

1. Get a filename or identifier as a string (say, from a save path or a model list).
2. Feed it into startswith with the prefix you care about - "output_", "flux", whatever.
3. Feed the BOOLEAN into an if/else or flow select node to route the graph down one path or another.

So "if the checkpoint starts with 'realvis', run the photorealistic post-processing branch, otherwise skip it" becomes a three-node chain instead of manual toggling. The Basic data handling pack is the same one that gives you those flow-control nodes, so everything stays on compatible types.

Installing it

Search "Basic data handling" in ComfyUI Manager and restart, or manually:

cd ComfyUI/custom_nodes
git clone https://github.com/StableLlama/ComfyUI-basic_data_handling

Restart, done. No dependencies beyond ComfyUI itself.

Gotchas

startswith is case-sensitive. "Flux" does not match the prefix "flux" - if you need case-insensitive routing, run the string through lower first and compare against a lowercased prefix. And remember it's an exact-prefix check, so a prefix of "a" matches any string that starts with a, and one of "abcdef" matches nothing in "abc". Short prefixes can match more than you intended; that's usually fine, but worth a glance at your data before you build a routing rule on it.