Next.js middleware executes before route handlers, enabling powerful patterns for authentication, internationalization, and request processing. Running at the edge provides low latency for these operations globally.
Common Use Cases
Authentication middleware validates sessions before allowing access. Redirect middleware handles URL changes and A/B testing. Header middleware adds security headers or modifies requests. Geolocation middleware personalizes based on location.
- Validate authentication tokens before protected routes
- Implement locale detection and redirect for i18n
- Add security headers consistently across all routes
- Handle legacy URL redirects without route handlers
- A/B test by routing to different page variants
Performance Considerations
Middleware runs on every matched request—keep it fast. Avoid heavy computation or external API calls. Use matcher configuration to limit middleware scope. Cache authentication validation results where possible.