Pick a month and year to see exactly how many days it has, the first and last weekday, and whether it is a leap February.
January, March, May, July, August, October and December have 31 days. April, June, September and November have 30. February has 28, or 29 in a leap year. This tool shows it for any month and year.
A year is a leap year if it is divisible by 4, except century years which must be divisible by 400. Pick February and a year and the tool tells you directly.
They are handy for planning, for example knowing a month starts on a Monday or ends on a weekend, when laying out calendars, rotas or pay periods.