Ask HN: Best way to document a new language's grammar?

Hey,

I'm in the process of writing the documentation for customer facing grammar (built using nearly.js) to allow for 'easy' querying of an API by the average Joe.

I was thinking of actually writing a GraphQL schema for the language's grammar and 'flattening' it out into a static page. Added plus is the schema can be used for autocomplete like behavior in a moded Graphiql IDE.

What documentation tools have you used in the past to document a language's grammar ? Would love your thoughts and feedback on how bad this idea is. Thanks !