I have a form wich contains some fields,when the user leaves one of these fields empty,I change the border color to red and I attached a red tooltip to explain the error ,is it possible to make tooltip as error message or should display a popup?
Keep error states visible so the users know what has happened. Don't leave users dependent on ephemeral elements like tooltips to understand what they have omitted or entered incorrectly.
In your form above, you're relying on a user having the cursor in the form input, or at least hovering above. What happens when they tab out?
You should also think of how to prevent an error in the first place.
You can do this by:
- Clear labeling
- Showing required fields
- Keeping input fields relative to the size of the characters allowed (as in numbers)
When users do have to deal with an error state, Nielsen Norman Group has some good resources of writing error messages.