| encoding/json | Package json implements encoding and decoding of JSON as defined in RFC 7159. |
| errors | Package errors implements functions to manipulate errors. |
| fmt | Package fmt implements formatted I/O with functions analogous to C's printf and scanf. |
| github.com/open-policy-agent/opa/v1/ast | Package ast declares Rego syntax tree types and also includes a parser and compiler for preparing policies for execution in the policy engine. |
| github.com/open-policy-agent/opa/v1/util | Package util provides generic utilities used throughout the policy engine. |
| math/big | Package big implements arbitrary-precision arithmetic (big numbers). |
| strings | Package strings implements simple functions to manipulate UTF-8 encoded strings. |