CodeIgniter is a PHP web framework built on the Model-View-Controller pattern, designed for building full-stack web applications. It provides a lightweight toolkit with minimal configuration, organizing application logic into controllers, models, and views for clean separation of concerns. The framework includes a fluent query builder for constructing SQL statements programmatically, PSR-4 autoloading with namespace mapping, and a service-based dependency injection container for managing shared class instances.
The framework distinguishes itself through its comprehensive set of built-in tools for common development tasks. It offers a complete CLI toolkit called Spark for code generation, database migrations, and task scheduling without external dependencies. For API development, CodeIgniter provides pre-built RESTful controllers with auto-routing, content negotiation for JSON and XML responses, and a full HTTP client for outbound requests. Security features include token-based CSRF protection, input validation and filtering, XSS prevention through context-aware escaping, and configurable Content Security Policy headers.
CodeIgniter includes a robust database abstraction layer with support for multiple drivers, schema management through migrations and seeding, and entity classes with automatic type casting and change detection. The framework provides session management with multiple storage backends, caching mechanisms for pages and data, and an event-driven lifecycle hook system. Additional capabilities cover email sending via multiple protocols, image manipulation, pagination, localization, and a debug toolbar for performance monitoring and request inspection.
The framework ships with a built-in testing toolkit that supports simulating HTTP requests, asserting responses, generating fake test data, and mocking application services. It can be installed via Composer or downloaded manually, and includes a development server command for local testing without a full web server setup.