| crypto/rand | Package rand implements a cryptographically secure random number generator. |
| encoding/json | Package json implements encoding and decoding of JSON as defined in RFC 7159. |
| fmt | Package fmt implements formatted I/O with functions analogous to C's printf and scanf. |
| io | Package io provides basic interfaces to I/O primitives. |
| strconv | Package strconv implements conversions to and from string representations of basic data types. |
| strings | Package strings implements simple functions to manipulate UTF-8 encoded strings. |