So we built a suite of tools to help with this called Rate My OpenAPI. It will score your OpenAPI document out of 100, as well as giving you individual scores in 4 key areas; completeness, SDK generation, security and documentation.
Along with the score, you also get details of what the issues, or errors are, as well as guidance on what they actually mean and why they're important.
We exposed the API for it using Zuplo, and then built a CLI, and a GitHub Action on top of that so that you can add Rate My OpenAPI into your workflow however you like.
You can check it out and use all of this right now, for free. I've already found it extremely useful and I hope you do to.
Feedback is absolutely welcome!