I started by attempting to extract the exiting JSON-LD hinter in use on the playground:
https://github.com/json-ld/json-ld.org/blob/master/playground/jsonld-hint.js

However, I quickly found that it's tightly coupled with the playground's assumptions (depends on jQuery, uses global variables from the playground, etc).

Consequently, I've started a new, more narrowly focused one:

• Demo: https://wileylabs.github.io/codemirror-jsonld-hint/
• Code: https://github.com/WileyLabs/codemirror-jsonld-hint

It's MIT licensed, and I'd love to make sure it provides the necessary extension points needed to provide a more widely usable JSON-LD linter--as I also have hopes of contributing this add-on upstream when it's "ready." 😸

So. Is there interest in such things? 😃

Thanks!
🎩