I built this because I kept running into dates on blogs, tickets, and documentation (e.g., "Due by Dec 25") and constantly had to switch context to open my calendar just to see what day of the week that falls on. I wanted a way to see that context without leaving the page.
The extension is lightweight (<50KB) and works by scanning the DOM for common date formats (ISO, US, EU). When it finds a match, it adds a subtle highlight. Hovering over the date reveals a tooltip with the day of the week (Monday, Tuesday, etc.).
If you have any feedback I would appreciate it!