This Language Server works for parsley files, which should have the .ply extension. It has the following language features:
Diagnostics, regenerated on each file change (save)
Linking to external files
Syntax highlighting for better development experience
Code Completion for NonTerminals, both those in standard library, and those defined by the user
It is necessary before using this extension, to have the parsley interpreter installed on your machine. This can easily be found here. Install this using the provided instructions, and then use the parsley.path::string setting to set where the executable can be found on your machine.