elysiajs

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---
name: elysiajs
description: Create backend with ElysiaJS, a type-safe, high-performance framework.
---

# ElysiaJS Development Skill

Always consult [elysiajs.com/llms.txt](https://elysiajs.com/llms.txt) for code examples and latest API.

## Overview

ElysiaJS is a TypeScript framework for building Bun-first (but not limited to Bun) type-safe, high-performance backend servers. This skill provides comprehensive guidance for developing with Elysia, including routing, validation, authentication, plugins, integrations, and deployment.

## When to Use This Skill

Trigger this skill when the user asks to:
- Create or modify ElysiaJS routes, handlers, or servers
- Setup validation with TypeBox or other schema libraries (Zod, Valibot)
- Implement authentication (JWT, session-based, macros, guards)
- Add plugins (CORS, OpenAPI, Static files, JWT)
- Integrate with external services (Drizzle ORM, Better Auth, Next.js, Eden Treaty)
- Setup WebSocket endpoints for real-time features
- Create unit tests for Elysia instances
- Deploy Elysia servers to production

## Quick Start
Quick scaffold:
```bash
bun create elysia app
```

### Basic Server
```typescript
import { Elysia, t, status } from 'elysia'

const app = new Elysia()
  	.get('/', () => 'Hello World')
   	.post('/user', ({ body }) => body, {
    	body: t.Object({
      		name: t.String(),
        	age: t.Number()
     	})
    })
    .get('/id/:id', ({ params: { id } }) => {
   		if(id > 1_000_000) return status(404, 'Not Found')
     
     	return id
    }, {
    	params: t.Object({
     		id: t.Number({
       			minimum: 1
       		})
     	}),
     	response: {
      		200: t.Number(),
        	404: t.Literal('Not Found')
      	}
    })
    .listen(3000)
```

## Basic Usage

### HTTP Methods
```typescript
import { Elysia } from 'elysia'

new Elysia()
  .get('/', 'GET')
  .post('/', 'POST')
  .put('/', 'PUT')
  .patch('/', 'PATCH')
  .delete('/', 'DELETE')
  .options('/', 'OPTIONS')
  .head('/', 'HEAD')
```

### Path Parameters
```typescript
.get('/user/:id', ({ params: { id } }) => id)
.get('/post/:id/:slug', ({ params }) => params)
```

### Query Parameters
```typescript
.get('/search', ({ query }) => query.q)
// GET /search?q=elysia → "elysia"
```

### Request Body
```typescript
.post('/user', ({ body }) => body)
```

### Headers
```typescript
.get('/', ({ headers }) => headers.authorization)
```

## TypeBox Validation

### Basic Types
```typescript
import { Elysia, t } from 'elysia'

.post('/user', ({ body }) => body, {
  body: t.Object({
    name: t.String(),
    age: t.Number(),
    email: t.String({ format: 'email' }),
    website: t.Optional(t.String({ format: 'uri' }))
  })
})
```

### Nested Objects
```typescript
body: t.Object({
  user: t.Object({
    name: t.String(),
    address: t.Object({
      street: t.String(),
      city: t.String()
    })
  })
})
```

### Arrays
```typescript
body: t.Object({
  tags: t.Array(t.String()),
  users: t.Array(t.Object({
    id: t.String(),
    name: t.String()
  }))
})
```

### File Upload
```typescript
.post('/upload', ({ body }) => body.file, {
  body: t.Object({
    file: t.File({
      type: 'image',              // image/* mime types
      maxSize: '5m'               // 5 megabytes
    }),
    files: t.Files({              // Multiple files
      type: ['image/png', 'image/jpeg']
    })
  })
})
```

### Response Validation
```typescript
.get('/user/:id', ({ params: { id } }) => ({
  id,
  name: 'John',
  email: '[email protected]'
}), {
  params: t.Object({
    id: t.Number()
  }),
  response: {
    200: t.Object({
      id: t.Number(),
      name: t.String(),
      email: t.String()
    }),
    404: t.String()
  }
})
```

## Standard Schema (Zod, Valibot, ArkType)

### Zod
```typescript
import { z } from 'zod'

.post('/user', ({ body }) => body, {
  body: z.object({
    name: z.string(),
    age: z.number().min(0),
    email: z.string().email()
  })
})
```

## Error Handling

```typescript
.get('/user/:id', ({ params: { id