| flag | Package flag implements command-line flag parsing. |
| fmt | Package fmt implements formatted I/O with functions analogous to C's printf and scanf. |
| math | Package math provides basic constants and mathematical functions. |
| math/rand | Package rand implements pseudo-random number generators suitable for tasks such as simulation, but it should not be used for security-sensitive work. |
| reflect | Package reflect implements run-time reflection, allowing a program to manipulate objects with arbitrary types. |
| strings | Package strings implements simple functions to manipulate UTF-8 encoded strings. |
| time | Package time provides functionality for measuring and displaying time. |