This is why we don't write date libraries Published 2025-09-12, About 8 minute read. I was assigned a pretty straightforward bug last week: we were miscalculating the end of day datetime. When a date was 2025-09-13T12:24:11.181+03:00 , we needed to check to see if that datetime was the "end of day" Why would need this? We needed to represent a date range up to and including a particular day. So…