8 Most Common PHP Code Mistakes of 2025 and How to Avoid Them

In 2025, many developers still make mistakes that cost time and security. Here are the 8 most common ones — with examples and solutions.

Mistakes and solutions

1. N+1 queries in loops
   Mistake: SELECT in foreach.
   Solution: eager loading or a single JOIN query.
   
2. Loose comparison (== instead of ===)
   Mistake: 0 == 'abc' returns true.
   Solution: Always use ===.
   
3. No type hints
   Mistake: Functions without types.
   Solution: Adding :array, :string, etc.
   
4. Direct use of $_POST without validation
   Mistake: SQL injection.
   Solution: PDO + prepared statements.
   
5. Ignoring Composer
   Mistake: require_once everywhere.
   Solution: PSR-4 autoloading.
   
6. Lack of error handling
   Error: try-catch only for PDO.
   Solution: global handler + logging.
   
7. Bad file structure
   Error: everything in one file.
   Solution: MVC or Service Layer.
   
8. Not using modern tools
   Error: no PHPStan/Rector.
   Solution: add to CI/CD.

Actionable tips

• Add PHPStan level 8 to your project.
  
• Run Rector for automatic correction.

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