Zettelkasten Linking Rules are the practices the Zettelkasten Method's own guide gives for connecting notes: each note gets a unique address, each new note is related to an existing one, and each link states why it was made.
In "Introduction to the Zettelkasten Method" (October 27, 2020), Sascha of zettelkasten.de writes that "A Zettelkasten makes connecting and not collecting a priority." The guide treats the identifier as mandatory: "Each Zettel needs a unique address by which we can refer to it, to make connections between Zettels." It suggests a time-stamp as a simple way to create one, and notes that a time-based ID never changes, so a title can be edited without breaking links. Placement matters less than addressability: "It is not important where you place a new note as long as you can link to it."
The guide also holds that "Each new Zettel needs to be placed in some relationship to another Zettel." On the link itself, it advises: "To make the most of a connection, always state explicitly why you made it." It calls this explanation the link context and warns that "If you just add links without any explanation you will not create knowledge."
For navigation, the guide describes structure notes: "A Structure Note is a Meta-Note: it is a Zettel about other Zettels and their relationships." It describes the approach of 📝Niklas Luhmann to fixed note addresses as a clever numbering system, and says Luhmann had hub notes that list many other places to look for the continuation of a topic. His register, in the guide's words, "is purely a list of entry points, not a tag list." After finding an entry, the guide says, he relied on the linking system. The broader method is covered in 📝Zettelkasten.