Introduction to Karin
What is Karin?
Karin is a TypeScript framework architected around the philosophy of "Complexity on Demand". It is designed to scale seamlessly from simple single-file scripts to complex, modular applications without imposing unnecessary rigid structures upfront.
While fully capable of powering production applications, Karin is primarily a personal learning project created to explore and master advanced software architecture patterns, such as:
- Dependency Injection (DI): Inversion of Control containers.
- Metadata Reflection: Decorator-based configuration.
- Modular Architecture: Structured separation of concerns.
- Platform Agnosticism: Native support for Bun, Cloudflare Workers, and Deno Deploy.
IMPORTANT
Karin is currently in active development (v0.5.x). While it offers a modern feature set comparable to established frameworks, it should be considered experimental.
Core Philosophy
Karin differs from other frameworks by striking a balance between structure and flexibility.
- Minimalist Core: The framework core is lightweight. You only pay the performance cost for features you actually import and use.
- Flexible Architecture: Unlike opinionated frameworks that mandate specific folder structures or modules, Karin adapts to the developer's needs. It supports both Automatic File Scanning (for rapid development in Bun) and Explicit Registration (for optimized Serverless/Edge deployments).
- Developer Experience (DX): Priorities include informative error messages, intuitive decorators, and first-class TypeScript support.
Comparison with NestJS
Developers coming from the NestJS ecosystem will find Karin familiar. It adopts similar architectural patterns (Controllers, Services, Guards) but with distinct design goals:
- Lighter: fast startup times and lower memory footprint.
- Simpler: No
AppModuleor complex module resolution logic is required by default. - Modern: Built from the ground up for modern runtimes like Bun and Edge environments.
Architecture Concept
To facilitate understanding of the framework's separation of concerns, the documentation occasionally refers to a "Restaurant Analogy".
Concept: The Restaurant Model
- The Request is the Order.
- The Controller is the Waiter: Receives the order, validates it, and passes it on. Does not cook.
- The Service is the Chef: Contains the "recipes" (business logic) and prepares the result.
- Karin is the Manager: Coordinates the staff (DI) and ensures resources are available.
Key Features
- Platform Agnostic: Optimized for Bun (native scanning), with full support for Cloudflare Workers and Deno Deploy via Hono/H3 adapters.
- Ecosystem Compatibility: The Hono adapter enables the usage of the vast library of existing Hono middleware.
- Dependency Injection: A robust DI container supporting Singleton and Transient scopes.
- Guards & Pipes: Comprehensive pipeline for request validation (e.g., Zod) and authorization.
- WebSockets: Bidirectional Real-time communication with built-in Room management.
- Plugin System: Extensible architecture supporting integrations like Drizzle, Redis, and more.
- Performance: Leverages high-performance underlying HTTP adapters (H3, Hono).
Next Steps
- Getting Started: Installation and your first endpoint.
- Architecture: A deep dive into the framework's internal design.
- TicketFlow Tutorial: Build a complete API from scratch.