1. What input requires inline validation?
2. For every input, do we have exact validation requirements?
3. What happens when a user jumps between empty fields?
4. What happens when a user jumps between incomplete fields?
5. What happens when a user jumps between invalid fields?
6. What happens when a user jumps between valid fields?
7. What happens when a user refreshes the page?
8. What happens when a user opens the page in another tab?
9. What happens if a user changes correct input?
10. What happens if a user changes incorrect input?
11. What input fields are likely to fail more often?
12. Can we break these fields into smaller ones to simplify validation?
13. For these fields, can we show input hints above them (under labels)?
14. Do we want to allow customers to proceed despite failed validation in these (or any other) fields?
15. If yes, do we ask users to confirm their input is correct?
16. For every input, do we set a minimum threshold of characters for validation to be triggered?
17. For every input, do we start validating only once that threshold is reached?
18. If there is an error, do we show it immediately as we detect it?
19. Or do we use only late validation (user has left the field, on blur)?
20. Do we avoid premature validation (on input focus)?
21. Do we avoid immediate validation (as a user starts typing)?
22. How do we minimize negative inline validation?
23. How do we maximize positive inline validation?
24. Do we never trigger new errors while the user fills in a form?
25. When editing a field that was valid, do we validate on blur?
26. When editing a field that was invalid, do we validate immediately during data entry?
27. Can we test a 'validate' button for complex input fields (passport number, IBAN, VAT, SMS code etc.)?
28. Can we use auto-suggestions or popular input to help fix mistakes faster?
29. How do we display error messages?
30. Do we announce error messages to screen readers?
31. Are error messages focusable?
32. Do we change the border/background of an invalid input field?
33. Do we display error messages above the input field?
34. Do we complement text messages with warning icons?
35. Does every error message drive a user towards fixing the error?
36. Do error messages change based on a user's specific errors?
37. Does every error message remain visible until the error is fixed?
38. Do error messages disappear only when input is validated?
39. Can we avoid disabled 'submit' buttons (and validate on submit)?
40. If not, can we explain why they are disabled and how to fix it?
41. Also, can we make disabled buttons focusable and provide help on tap/click/tab?
42. If yes, can we show a tooltip linking to the error at the top?
43. Can we guide users to errors when they submit?
44. When should we guide users to the error summary at the top instead?
45. Or do we auto-scroll the user to the label of the first error?
46. In the error summary, do we display each error as a line on its own?
47. Do we have server-side validation as well?
48. Do we indicate failed validation in the browser tab's title (e.g., error count and emoji)?
49. Do we monitor error rates to track how often users experience errors?
50. Do we maintain and refine the wording of error messages over time?