HTML Validation Guide

Why Validation Matters

HTML validation ensures data quality, improves security, and enhances user experience. This guide covers native HTML5 validation attributes, custom validation techniques, and best practices for modern web development.

1. Client-Side Validation

HTML5 Attributes


  
    Email *
    
  
  
    Password *

required

pattern

JavaScript Enhancements

document.querySelector('form').addEventListener('submit', function(e) {
  const password = document.getElementById('password');
  if (password.value.length < 8) {
    e.preventDefault();
    alert('Password must be at least 8 characters');
  }
});

🔧 Combine with HTML5 attributes for enhanced client-side validation

2. Server-Side Validation (PHP Example)

$valid = true;
if (!filter_var($_POST['email'], FILTER_VALIDATE_EMAIL)) {
  echo "⚠️ Email format invalid";
  $valid = false;
}

if (strlen($_POST['password']) < 8) {
  echo "⚠️ Password too short";
  $valid = false;
}

if ($valid) {
  // Process form
}

3. Visual Feedback Patterns

Inline Validation

Invalid email format

Summary Feedback

Email format invalid
Password too short

Best Practices

Layered Defense

Always implement client-server validation tandem

Progressive Feedback

Show errors immediately but in batches

Security First

Never trust user input - validate everything