| fmt | Package fmt implements formatted I/O with functions analogous to C's printf and scanf. |
| go/token | Package token defines constants representing the lexical tokens of the Go programming language and basic operations on tokens (printing, predicates). |
| math | Package math provides basic constants and mathematical functions. |
| math/big | Package big implements arbitrary-precision arithmetic (big numbers). |
| strconv | Package strconv implements conversions to and from string representations of basic data types. |
| unicode/utf8 | Package utf8 implements functions and constants to support text encoded in UTF-8. |