| 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/ast | Package ast declares the types used to represent syntax trees for Go packages. |
| go/build/constraint | Package constraint implements parsing and evaluation of build constraint lines. |
| go/doc/comment | Package comment implements parsing and reformatting of Go doc comments, (documentation comments), which are comments that immediately precede a top-level declaration of a package, const, func, type, or var. |
| go/token | Package token defines constants representing the lexical tokens of the Go programming language and basic operations on tokens (printing, predicates). |
| io | Package io provides basic interfaces to I/O primitives. |
| math | Package math provides basic constants and mathematical functions. |
| os | Package os provides a platform-independent interface to operating system functionality. |
| sort | Package sort provides primitives for sorting slices and user-defined collections. |
| 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. |
| text/tabwriter | Package tabwriter implements a write filter (tabwriter.Writer) that translates tabbed columns in input into properly aligned text. |
| 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. |