The quickest route for feedback, questions and bug reports is a GitHub issue. An issue is public, so others can see the answer and add to it. Pick the route that fits:

• A bug, unclear wording, or a question about the schema: open an issue.
• A change you'd like to make: open a pull request. The contributing guide says what a change needs.
• A security problem in the specification, a validator or this site: report it privately through the repository's security advisories. Don't open a public issue for it. Include what you found, how to reproduce it, and its impact if you can.
• Anything that doesn't fit on GitHub: email pj@pjonori.com.

This is a one-person project, so there's no response-time guarantee. Security reports are read first, and a fix or mitigation is the priority as soon as one is found.