Elysia
TypeScript framework for Bun with end-to-end type safety
Overview
Elysia is built specifically for the Bun runtime, leveraging Bun's speed advantages to deliver exceptional performance. The framework achieves end-to-end type safety by inferring types from your route definitions through response handlers - no manual type annotations needed for the common cases.
The developer experience is where Elysia truly differentiates. The API reads almost like pseudocode - define a route, add validation, and the types flow through automatically. Input validation, output types, and OpenAPI documentation are all derived from the same source of truth.
The plugin system enables composition without complexity. Authentication, rate limiting, CORS, and database connections all plug in cleanly, with types propagating through the entire chain. Adding a feature does not mean rewriting your type definitions.
Key Features
End-to-End Types
Automatic type inference from routes through responses
Bun Optimized
Built for Bun runtime with exceptional performance
Validation
Request and response validation with automatic type narrowing
OpenAPI Generation
Automatic API documentation from route definitions
Plugin Composition
Type-safe plugins that propagate types through the chain
Eden Client
Type-safe client for calling your API from the frontend
Why We Recommend Elysia
Elysia offers the best developer experience of any backend framework we have used. For Bun-based projects where type safety and ergonomics matter, it makes building APIs genuinely enjoyable.