Add the following JSON to your `.arclint`:
```lang=json
"rubocop": {
"type": "rubocop",
"include": "(\\.rb$)"
}
```
Then, add a ruby file with errors, for instance:
```lang=ruby
def hello()
puts 'world'
end
```
Run `arc lint`. It should come up with something along the line of: "Omit the parentheses in defs when the method doesn't accept any arguments."