...

Help text adjacent to input fields is most useful when it's:

1. Unfamiliar data

   You ask the user for unfamiliar data (User might ask “What’s this?”)
   For example, it's not obvious where the users can find a barcode and concise help text next to the input field might be very helpful.
   
   
   

2. Specific data

   People might question why you are asking for specific data
    
   
   

3. Concerns about security or privacy

   People may be concern about the security or privacy of their data and you need to reassure them that the data won’t be shared with 3rd party sources.
   
   
   

4. Helpful information in context

   Sometimes you need to have relevant, in-context information ready to assist users to move through the form easily. For example, when scheduling dates, users appreciate context like a monthly calendar to identify days of the week, eliminating the need to leave the app to check the smartphone’s calendar. It also reduces the risk of the user becoming distracted by another task.
   

Don't Hide

Password Rules

Tell users what your password rules are up front, rather than making them guess and wait for validation errors.

...