Privacy
Marklet collects nothing. There are no accounts, no analytics, no telemetry, and no crash reporting. Your documents are plain text files on your Mac, and they stay there.
Update checks
The direct-download version of Marklet checks GitHub for new versions (using the Sparkle framework). That request is an ordinary download from GitHub's servers, subject to GitHub's privacy statement; Marklet sends nothing about you or your documents with it. Automatic checking can be turned off in Settings. The Mac App Store version performs no update checks of its own.
This website
This site sets no cookies and runs no analytics. Fonts are served by Google Fonts, which involves an ordinary font file request to Google's servers.
Questions
Open an issue on GitHub or email wakmail.dev@gmail.com.