A frozen string is a string literal object that is compatible with the managed heap and has been serialized into a native image by the Native Image Generator (Ngen.exe). The System.Runtime.CompilerServices.StringFreezingAttribute attribute allows you to optimize your code by pre-allocating string literals during native image generation rather than at run time. After a string literal has been frozen, code can simply refer to the string using the address in the native image.

The System.Runtime.CompilerServices.StringFreezingAttribute must be applied on the assembly level.

Note that the common language runtime (CLR) cannot unload any native image that has a frozen string because any object in the heap might refer to the frozen string. Therefore, you should use the System.Runtime.CompilerServices.StringFreezingAttribute class only in cases where the native image that contains the frozen string is shared heavily.