Elysia Skill

Expert knowledge for building high-performance, type-safe web applications with ElysiaJS - a fast, ergonomic Bun web framework with end-to-end type safety.

This skill synthesizes knowledge from official Elysia documentation covering core concepts, patterns, plugins, and integrations.

When to Use This Skill

This skill should be triggered when you are:

Building Web APIs:

• Creating RESTful APIs with Elysia
• Setting up HTTP routes (GET, POST, PUT, DELETE, etc.)
• Implementing request/response handlers
• Working with route parameters, query strings, or request bodies

Type Safety & Validation:

• Adding schema validation with Elysia.t (TypeBox)
• Using Standard Schema validators (Zod, Valibot, ArkType, etc.)
• Validating request bodies, queries, params, headers, or cookies
• Generating OpenAPI documentation from schemas

Lifecycle Hooks & Middleware:

• Implementing authentication/authorization checks
• Adding logging, error handling, or request preprocessing
• Using lifecycle hooks (beforeHandle, afterResponse, onError, etc.)
• Creating reusable route options with Macros

End-to-End Type Safety:

• Setting up Eden Treaty for type-safe client-server communication
• Exporting server types for frontend consumption
• Creating type-safe API clients (similar to tRPC)
• Testing with end-to-end type safety

Framework Integrations:

• Integrating Elysia with Next.js, Nuxt, SvelteKit, Astro, or Expo
• Setting up Drizzle ORM with Elysia
• Using AI SDK with Elysia for streaming responses
• Deploying to Netlify Edge Functions or other platforms

Plugin Development:

• Creating custom Elysia plugins
• Using official plugins (@elysiajs/*)
• Implementing OpenTelemetry for observability
• Working with HTML, CORS, JWT, GraphQL, or other plugins

Key Concepts

Method Chaining

Elysia uses method chaining extensively. Each method returns a new instance with updated types:

new Elysia()
  .state('version', 1)
  .get('/', ({ store }) => store.version)
  .listen(3000)

Important: Always use method chaining - it's required for proper type inference, especially with Eden.

Schema Validation

Elysia provides t (TypeBox) for runtime and compile-time type safety. Schemas automatically generate TypeScript types and OpenAPI documentation:

import { Elysia, t } from 'elysia'

new Elysia()
  .post('/user', ({ body }) => body, {
    body: t.Object({
      name: t.String(),
      age: t.Number()
    })
  })

Lifecycle Hooks

Hooks execute at specific points in the request-response cycle:

• request - when request is received
• beforeHandle - before executing handler (e.g., auth checks)
• afterHandle - after handler, before response
• afterResponse - after response is sent
• onError - when errors occur

Hooks can be local (specific route) or interceptor (all routes after registration).

Eden Treaty

Eden provides end-to-end type safety between server and client, similar to tRPC but using Elysia's type system:

// server.ts
const app = new Elysia()
  .get('/user/:id', ({ params: { id } }) => ({ id, name: 'John' }))
export type App = typeof app

// client.ts
import { treaty } from '@elysiajs/eden'
const api = treaty<App>('localhost:3000')
const { data } = await api.user({ id: '1' }).get()
// data is fully typed!

Quick Reference

1. Basic Server Setup

import { Elysia } from 'elysia'

new Elysia()
  .get('/', () => 'Hello Elysia')
  .listen(3000)

console.log('🦊 Elysia is running at http://localhost:3000')

2. Route with Validation

import { Elysia, t } from 'elysia'

new Elysia()
  .post('/user', ({ body }) => body, {
    body: t.Object({
      name: t.String(),
      email: t.String({ format: 'email' })
    })
  })
  .listen(3000)

3. Path Parameters & Query Strings

import { Elysia, t } from 'elysia'

new Elysia()
  .get('/id/:id', ({ params: { id }, query }) => {
    return { id, query }
  }, {
    params: t.Object({
      id: t.Number() // Automatically coerced from string
    }),
    query: t.Object({
      name: t.String()
    })
  })
  .listen(3000)

4. Authentication with beforeHandle Hook

import { Elysia } from 'elysia'

new Elysia()
  .onBeforeHandle(({ query: { name }, status }) => {
    if (!name) return status(401)
  })
  .get('/protected', ({ query: { name } }) => {
    return `Welcome ${name}!`
  })
  .listen(3000)

5. Local Hook for Specific Route

import { Elysia } from 'elysia'

new Elysia()
  .get('/public', () => 'Public route')
  .get('/auth', () => 'Authenticated!', {
    beforeHandle({ request, status }) {
      if (Math.random() <= 0.5) return status(418)
    }
  })
  .listen(3000)

6. Guard for Multiple Routes

import { Elysia, t } from 'elysia'

new Elysia()
  .get('/none', () => 'No validation')
  .guard({
    query: t.Object({
      name: t.String()
    })
  })
  .get('/query', ({ query: { name } }) => name)
  .get('/query2', ({ query: { name } }) => `Hello ${name}`)
  .listen(3000)

7. State Management

import { Elysia } from 'elysia'

new Elysia()
  .state('count', 0)
  .get('/', ({ store }) => {
    store.count++
    return store.count
  })
  .listen(3000)

8. Custom Status & Redirect

import { Elysia } from 'elysia'

new Elysia()
  .get('/teapot', ({ status }) => status(418, "I'm a teapot"))
  .get('/home', ({ redirect }) => redirect('https://elysiajs.com'))
  .listen(3000)

9. Reusable Macro

import { Elysia, t } from 'elysia'

new Elysia()
  .macro('auth', {
    cookie: t.Object({
      session: t.String()
    }),
    beforeHandle({ cookie: { session }, status }) {
      if (!session.value) return status(401)
    }
  })
  .post('/user', ({ body }) => body, {
    auth: true // Applies auth macro
  })
  .listen(3000)

10. Eden Setup (End-to-End Type Safety)

Server:

// server.ts
import { Elysia, t } from 'elysia'

const app = new Elysia()
  .get('/', () => 'Hi Elysia')
  .get('/id/:id', ({ params: { id } }) => id)
  .post('/mirror', ({ body }) => body, {
    body: t.Object({
      id: t.Number(),
      name: t.String()
    })
  })
  .listen(3000)

export type App = typeof app

Client:

bun add @elysiajs/eden
bun add -d elysia

// client.ts
import { treaty } from '@elysiajs/eden'
import type { App } from './server'

const api = treaty<App>('localhost:3000')

const { data, error } = await api.mirror.post({
  id: 1,
  name: 'Elysia'
})

if (error) console.error(error.value)
else console.log(data) // Fully typed!

11. Error Handling

import { Elysia, t } from 'elysia'

new Elysia()
  .get('/:id', ({ params: { id } }) => id, {
    params: t.Object({
      id: t.Number({
        error: 'id must be a number'
      })
    })
  })
  .onError(({ code, error, status }) => {
    if (code === 'VALIDATION')
      return status(400, error.message)

    return status(500, 'Internal Server Error')
  })
  .listen(3000)

12. Standard Schema (Zod Example)

import { Elysia } from 'elysia'
import { z } from 'zod'

new Elysia()
  .post('/user', ({ body }) => body, {
    body: z.object({
      name: z.string(),
      age: z.number()
    })
  })
  .listen(3000)

13. Drizzle ORM Integration

bun add drizzle-orm drizzle-typebox

import { Elysia } from 'elysia'
import { drizzle } from 'drizzle-orm/bun-sqlite'
import { createInsertSchema } from 'drizzle-typebox'
import { users } from './schema'

const db = drizzle(/* ... */)
const insertUserSchema = createInsertSchema(users)

new Elysia()
  .post('/user', async ({ body }) => {
    const user = await db.insert(users).values(body)
    return user
  }, {
    body: insertUserSchema
  })
  .listen(3000)

14. File Upload

import { Elysia, t } from 'elysia'

new Elysia()
  .post('/upload', async ({ body: { file } }) => {
    return `Uploaded: ${file.name}`
  }, {
    body: t.Object({
      file: t.File()
    })
  })
  .listen(3000)

15. Plugin Creation

import { Elysia } from 'elysia'

const myPlugin = new Elysia({ name: 'my-plugin' })
  .state('pluginVersion', '1.0.0')
  .get('/plugin', ({ store }) => store.pluginVersion)

new Elysia()
  .use(myPlugin)
  .listen(3000)

Reference Files

This skill includes comprehensive documentation extracted from official Elysia sources. All examples and information come from official documentation (medium-high confidence).

references/essential.md (6 pages)

Core Elysia concepts including:

• Validation - TypeBox schemas, Standard Schema support (Zod, Valibot, etc.)
• Lifecycle - Request-response cycle, hooks, and middleware
• Body/Query/Params - Request data validation
• Guard - Apply schemas to multiple routes

references/eden.md (11 pages)

End-to-end type safety with Eden:

• Installation - Setup Eden Treaty on frontend
• Type Inference - Gotchas and troubleshooting
• Testing - Unit testing with Eden
• Treaty API - Tree-like syntax, dynamic paths, responses

references/tutorial.md (14 pages)

Step-by-step guides including:

• Getting Started - Basic server setup
• Lifecycle Hooks - Local vs interceptor hooks
• Mount - Composing multiple Elysia instances
• Features - Advanced patterns and techniques

references/patterns.md (21 pages)

Advanced patterns including:

• Macro - Reusable route options
• Error Handling - Custom errors, validation messages
• Configuration - Server configuration options
• OpenTelemetry - Observability integration

references/plugins.md (13 pages)

Official plugins documentation:

• OpenTelemetry - Distributed tracing
• HTML - Server-side rendering
• CORS - Cross-origin resource sharing
• JWT - JSON Web Token authentication
• GraphQL - GraphQL integration

references/integrations.md (17 pages)

Framework integrations:

• Drizzle ORM - Database integration with type safety
• Next.js - Integration with Next.js App Router
• Nuxt - Integration with Nuxt 3
• SvelteKit - Integration with SvelteKit
• Expo - React Native integration
• Astro - Integration with Astro
• AI SDK - Streaming AI responses

references/other.md

Additional topics and utilities.

Working with This Skill

For Beginners

1. Start with basics - Read references/tutorial.md for getting started guides
2. Learn validation - Check references/essential.md for schema validation
3. Try examples - Use the Quick Reference examples above to build your first server
4. Understand hooks - Learn lifecycle hooks for middleware and authentication

For Intermediate Users

1. Master Guards - Apply schemas to multiple routes efficiently
2. Use Macros - Create reusable route options for common patterns
3. Add Eden - Implement end-to-end type safety with Eden Treaty
4. Error handling - Implement robust error handling with custom errors

For Advanced Users

1. Create plugins - Build reusable Elysia plugins for your organization
2. Integrate frameworks - Connect Elysia with Next.js, Nuxt, or other frameworks
3. Add observability - Implement OpenTelemetry for distributed tracing
4. Optimize performance - Use Elysia's ahead-of-time compilation features

Navigation Tips

• Need validation help? → references/essential.md
• Setting up Eden? → references/eden.md
• Framework integration? → references/integrations.md
• Creating plugins? → references/plugins.md
• Advanced patterns? → references/patterns.md
• Learning the basics? → references/tutorial.md

Important Notes

TypeScript Requirements

• Minimum TypeScript version: 5.0+
• Enable strict mode in tsconfig.json
• Method chaining is required for proper type inference

Eden Gotchas

• Server and client must have matching Elysia versions
• Use method chaining - required for type inference
• Pin @sinclair/typebox version if using Drizzle
• Path aliases in monorepos need careful configuration

Validation Best Practices

• Use t.File() for file uploads (sets content-type automatically)
• Validation details are hidden in production by default
• Custom error messages can be set per field
• Standard Schema (Zod, Valibot, etc.) is fully supported

Performance Tips

• Elysia runs on Bun for maximum performance
• Ahead-of-time compilation optimizes route handlers
• Use guards to apply validation to multiple routes efficiently
• State is instance-scoped, not request-scoped

Source Information

All content synthesized from official Elysia documentation:

• Source Type: Official Documentation
• Confidence: Medium-High
• Documentation URL: https://elysiajs.com

No conflicts detected between sources. All examples and patterns come directly from official Elysia documentation and are considered authoritative.

Additional Resources

Installation

bun add elysia

Common Plugins

# Eden (type-safe client)
bun add @elysiajs/eden

# HTML rendering
bun add @elysiajs/html

# CORS
bun add @elysiajs/cors

# JWT
bun add @elysiajs/jwt

# GraphQL
bun add @elysiajs/graphql-yoga

# OpenTelemetry
bun add @elysiajs/opentelemetry

Community

• Official Website: https://elysiajs.com
• GitHub: https://github.com/elysiajs/elysia
• Discord: Join the Elysia community for support

Updating

This skill was automatically generated from official Elysia documentation. To refresh:

1. Re-run the documentation scraper with the same configuration
2. The skill will be rebuilt with the latest information
3. All reference files will be updated with new examples and patterns