| bytes | Package bytes implements functions for the manipulation of byte slices. |
| fmt | Package fmt implements formatted I/O with functions analogous to C's printf and scanf. |
| go/constant | Package constant implements Values representing untyped Go constants and their corresponding operations. |
| go/format | Package format implements standard formatting of Go source. |
| go/token | Package token defines constants representing the lexical tokens of the Go programming language and basic operations on tokens (printing, predicates). |
| go/types | Package types declares the data types and implements the algorithms for type-checking of Go packages. |
| io | Package io provides basic interfaces to I/O primitives. |
| log | Package log implements a simple logging package. |
| math | Package math provides basic constants and mathematical functions. |
| regexp | Package regexp implements regular expression search. |
| strings | Package strings implements simple functions to manipulate UTF-8 encoded strings. |
| unicode | Package unicode provides data and functions to test some properties of Unicode code points. |
| unicode/utf8 | Package utf8 implements functions and constants to support text encoded in UTF-8. |