Kirchhoff's rules can be applied to any circuit since they are applications to circuits of two conservation laws. Conservation laws are the most broadly applicable principles in physics.

Does Kirchhoff's rule always apply?

Kirchhoff's rules can be applied to any circuit, regardless of its composition and structure. Because combining elements is often easy in parallel and series, it is not always convenient to apply Kirchhoff's rules. To solve for current in a circuit, the loop and junction rules can be applied.

Are Kirchhoff rules applicable to both AC and DC?

Kirchhoff's laws are applicable for DC as well as AC circuits. They can be accurately used for DC circuits and low-frequency AC circuits.