What is the smallest cake decorating tip?

The smallest cake decorating tip depends on what you mean by "smallest." Do you mean:

* Smallest diameter opening? There are tips with openings as small as 1 mm. These are typically used for intricate details, writing, or creating very fine lines.

* Smallest tip number? The smallest tip number varies depending on the brand, but you can find tips with numbers like #1, #2, #3, and even smaller. These tips generally have smaller openings than larger numbers.

* Smallest overall size? Some micro-tips or fine detail tips are designed to be very small and precise, even if their opening isn't necessarily the absolute smallest.

To get the most accurate answer, you need to specify what you're looking for. If you could tell me the kind of detail you're trying to create, I can give you a more precise recommendation for the smallest tip you should use.