They can also be run locally on your machine using the

[`opa eval` command, here are setup instructions.](#running-opa)

Note that the examples in this section try to represent the best practices.

As such, they make use of keywords that are meant to become standard keywords

at some point in time, but have been introduced gradually.

[See the docs on_future keywords_](./docs/policy-language/#future-keywords)

for more information.

The simplest way to interact with OPA is via the command-line using the[`opa eval` sub-command](./docs/cli/#opa-eval).

The simplest way to interact with OPA is via the command-line using the[`opa eval` sub-command](./docs/cli#eval).

It is a swiss-army knife that you can use to evaluate arbitrary Rego expressions and policies.

`opa eval` supports a large number of options for controlling evaluation.

Commonly used flags include:

OPA includes an interactive shell or REPL (Read-Eval-Print-Loop) accessible via

the[`opa run` sub-command](./docs/cli/#opa-run).

the[`opa run` sub-command](./docs/cli#run).

You can use the REPL to experiment with policies and prototype new ones.

To start the REPL just: