Context-Specific Validation Rules

Different contexts within your application require different validation rules. A field that accepts usernames has different requirements than one accepting blog post content. Create context-specific validators that understand these differences. This might mean having separate validation classes for different types of input or configurable validators that accept context-specific rules.

For API endpoints, implement strict validation of both structure and content. Use schema validation libraries to ensure requests match expected formats. This includes validating JSON structure, required fields, data types, and value constraints. Modern frameworks often provide request validation middleware that can automatically validate incoming requests against defined schemas. This automated validation reduces the chance of developers forgetting to validate specific fields.

File upload validation requires special attention as files can contain various types of malicious content. Validate file types by checking magic numbers (file signatures) rather than relying on extensions, which are easily spoofed. Implement size limits to prevent denial of service. For image uploads, re-encode images to strip potentially malicious metadata. Never serve uploaded files from your main domain – use a separate domain or Content Delivery Network to isolate potential XSS payloads in uploaded content.