How Leap year checker works
Leap year checker tells you whether a given year is a leap year, and explains why, using the actual Gregorian rule (divisible by 4, except centuries unless divisible by 400). It also lists the nearest leap years around the one you entered.
Where Date details mentions leap-year status as one fact among many, this tool focuses on the rule itself, making it the right page for the query "is 2100 a leap year?" and for understanding the reasoning. It also lists the nearest leap years on either side of the one you entered.