StartLoop - ComfyUI Built-in Node Documentation

The Start Loop node starts a looping structure inside a workflow. It runs the connected loop body one time per iteration and can count iterations in three ways: a fixed number of repetitions (simple), a numeric index range (For), or one pass per item in a list (List). Each pass exposes the current index, first/last flags, and an optional carried value that can be passed from one iteration to the next.

Inputs

Common Inputs

Parameter	Description	Data Type	Required	Range
`mode`	The loop iteration mode (default: “simple”). The selected mode determines which additional parameters are shown.	DYNAMIC_COMBO	Yes	`"simple"` `"For"` `"List"`
`cache_iterations`	Reuse unchanged iteration results from previous executions. Disable to execute every iteration again. Default: false.	BOOLEAN	Yes	true false
`parent_iteration`	Connect iteration_index from an outer Start Loop to nest this loop. This input is force-input only (a link is required).	INT	No	Any integer
`initial_iteration_value`	Value exposed as current_iteration_value on the first iteration.	ANY (type-matched)	No	Any value

Simple Mode Inputs

Parameter	Description	Data Type	Required	Range
`num_iterations`	Number of times to execute the loop body. Default: 4.	INT	Yes	Minimum 0

For Mode Inputs

Parameter	Description	Data Type	Required	Range
`start_iteration_index`	Index of the first iteration when using For loop mode. Default: 0.	INT	Yes	Any integer
`max_iteration`	The exclusive stopping value for iteration_index in For mode. Default: 4.	INT	Yes	Maximum 0xffffffffffffffff
`step`	The index step size between each iteration when using For loop mode. Default: 1.	INT	Yes	Minimum 1

List Mode Inputs

Parameter	Description	Data Type	Required	Range
`list`	List of items the loop iterates on. The loop body executes once per item.	ANY (type-matched list item)	Yes	Any list

Notes:

Only the parameters belonging to the currently selected mode are shown and used.
In Simple mode, the iteration indices run from 0 up to num_iterations minus 1. In For mode, indices run from start_iteration_index up to (but not including) max_iteration, increasing by step. In List mode, one iteration runs per item in list.
step must not be 0; a value of 0 raises an error. Values below 1 are not allowed.
If the computed number of iterations is zero, the is_last output is reported as true and the loop body does not run.

Outputs

Output Name	Description	Data Type
`iteration_index`	Index of the current loop iteration.	INT
`is_first`	True during the first iteration of the loop.	BOOLEAN
`is_last`	True during the last iteration of the loop.	BOOLEAN
`list_item`	Current item from the list when using List mode. None in Simple and For modes.	ANY (type-matched)
`current_iteration_value`	Loop-carried value for the current iteration: initial_iteration_value on the first iteration, then next_iteration_value from End Loop on each subsequent iteration.	ANY (type-matched)

This documentation was AI-generated. If you find any errors or have suggestions for improvement, please feel free to contribute! Edit on GitHub

Source fingerprint (SHA-256): be34fedd4db9d4f4cc795855c87f6489f294e029da316b5dc66e5af7dff004a9

​Inputs

​Common Inputs

​Simple Mode Inputs

​For Mode Inputs

​List Mode Inputs

​Outputs