Introduction

HTML has built-in form validation that runs automatically in the browser — no JavaScript needed. These features prevent invalid input, ensure correct formatting, and improve form usability instantly.

1. Required Fields

Browser will block submission if empty.

2. Email Validation

Checks format like name@example.com.

3. Min and Max Length

4. Number Ranges

5. Pattern Validation (Regex)

Force custom formats.

6. Password Example

Requires: - 8+ characters - one uppercase - one digit

7. Matching Passwords (using JS lightly)

8. URL Validation

9. Telephone Patterns

10. Auto Validation on Submit

  
  Submit

    

The browser pops built-in warnings automatically.

11. Custom Error Messages

12. novalidate (Disable HTML Validation)

Useful when using your own JS validation.

13. Using title for Error Hints

14. Client + Server Validation Combo

• HTML → fast, user-friendly checks
• Server → final validation for security

Common Mistakes

• Relying only on client-side validation
• Not validating server-side
• Using too strict regex patterns
• Missing helpful error messages

Summary

• required, min, max, pattern control input rules
• Browsers enforce validation automatically
• Use custom messages for clarity
• Always validate again on the server