在编码理论，克拉夫特不等式给出了一个码字长度集合存在唯一可解编码/单义可译码（uniquely decodable code）的必要条件。因为这个不等式在前缀码和树上面应用很多，所以在计算机科学和信息学中很常用。

克拉夫特不等式对码字限制长度以保证前缀编码的可能性。这个不等式说明码字长度指数的倒数的分布和概率质量函数很相似。克拉夫特不等式can be thought of in terms of a constrained budget to be spent on codewords, with shorter codewords being more expensive.

In coding theory, Kraft's inequality, named after Leon Kraft, gives both a necessary and sufficient condition for the existence of a prefix code for a given set of codeword lengths. Its applications to prefix codes and trees often find use in computer science and information theory.