There is no enforced standard for passwords for a web site, so they can be all over the place for requirements. Nor do sites typically explain what are the exact standards before a failure. And then most will state the minimum and types of characters. But, too many leave out the maximum number of characters allowed so I end up experimenting to figure out something as strong as I can get. One of my favorite blogs is Password Requirements Shaming.
Web sites almost certainly record the password to a variable. Hopefully they then encrypt it and store the hash instead of recording the password as plain text. I use LastPass’ password generator to create something typically 40 characters  long and try it. Almost always that results in an error that my password is too long and the limit is actually something shorter. There are some frustrations with how sites handle these cases:
- In HTML, maxlength defines how many characters the input element will accept. I sometimes look at the HTML to select what password length to generate, but there is no guarantee that the maxlength is reflective of what will work. It fails to help so much I have gotten out of the habit.
Arbitrariness with password policies probably makes people tend to more insecure practices through simplification. This is The Paradox of Choice.
It occurred to me that LastPass developers could solve this problem for me. If LastPass knew the password requirements for a site, then it could preset the generator to the maximum length that will fit. When I go to create a password for a site, then it could work the first time instead of taking 2-5 tries to find something that finally works. Most users are lazy and would not change the preset, so passwords would tend to be the stronger. 
Admittedly, it usually works on the second try once I’ve nailed down the maximum number of characters allowed.
 See Nudge: Improving Decisions About Health, Wealth, and Happiness for how organ donation rates work for how t his would work.
From LastPass feature request published January 10, 2017 at 07:20AM.