HTML Form Validation
Learn how to validate user input directly in the browser with HTML5 validation features.
What is Form Validation?
Form validation ensures that users enter data in the correct format before submitting. HTML5 provides built-in validation features that work without JavaScript!
ā Client-Side Benefits
- Instant feedback to users
- Reduced server load
- Better user experience
- No JavaScript required
- Accessible by default
šÆ Common Use Cases
- Required field checking
- Email format validation
- Password strength
- Number range validation
- Custom pattern matching
Important: Always validate on the server too! Client-side validation can be bypassed.
š Quick Reference
requiredMakes field mandatory
type="email"Email format validation
pattern="regex"Custom pattern matching
minlength="n"Minimum characters
novalidateDisable browser validation
šļø Validation States
Valid Input
Field meets all validation criteria
Invalid Input
Field fails validation rules
Pending Validation
User hasn't interacted yet
š¤ Common Patterns
[A-Za-z0-9]+Letters and numbers only
\d{5}(-\d{4})?US ZIP code
[A-Za-z]{2}Two-letter state code
\+?[\d\s-()]+Phone number
[A-Za-z]{3,15}Username (3-15 letters)