hono-routing

name	hono-routing
description	Build type-safe APIs with Hono for Cloudflare Workers, Deno, Bun, Node.js. Routing, middleware, validation (Zod/Valibot), RPC, streaming (SSE), WebSocket, security (CSRF, secureHeaders).
license	MIT
compatibility	agents
metadata	{"audience":"backend-developers, full-stack-engineers, api-developers","domain":"api-development, backend-development"}

Hono Routing & Middleware

What I do

Provide production-ready patterns for building type-safe APIs with Hono, including routing, middleware chains, request validation, RPC patterns, and advanced features like streaming and WebSocket support.

When to use me

Use this skill when:

• Building Hono APIs for any JavaScript runtime
• Implementing request validation with Zod/Valibot
• Setting up type-safe RPC client/server patterns
• Creating streaming endpoints (SSE, AI responses)
• Implementing WebSocket connections
• Configuring security middleware (CSRF, headers)

Status: Production Ready ✅ Last Updated: 2026-01-20 Dependencies: None (framework-agnostic) Latest Versions: hono@4.11.4, zod@4.3.5, valibot@1.2.0, @hono/zod-validator@0.7.6, @hono/valibot-validator@0.6.1

---

Quick Start (15 Minutes)

1. Install Hono

npm install hono@4.11.4

Why Hono:

• Fast: Built on Web Standards, runs on any JavaScript runtime
• Lightweight: ~10KB, no dependencies
• Type-safe: Full TypeScript support with type inference
• Flexible: Works on Cloudflare Workers, Deno, Bun, Node.js, Vercel

2. Create Basic App

import { Hono } from 'hono'

const app = new Hono()

app.get('/', (c) => {
  return c.json({ message: 'Hello Hono!' })
})

export default app

CRITICAL:

• Use c.json(), c.text(), c.html() for responses
• Return the response (don't use res.send() like Express)
• Export app for runtime (Cloudflare Workers, Deno, Bun, Node.js)

3. Add Request Validation

npm install zod@4.3.5 @hono/zod-validator@0.7.6

import { zValidator } from '@hono/zod-validator'
import { z } from 'zod'

const schema = z.object({
  name: z.string(),
  age: z.number(),
})

app.post('/user', zValidator('json', schema), (c) => {
  const data = c.req.valid('json')
  return c.json({ success: true, data })
})

Why Validation:

• Type-safe request data
• Automatic error responses
• Runtime validation, not just TypeScript

---

The 4-Part Hono Mastery Guide

Part 1: Routing Patterns

Route Parameters

// Single parameter
app.get('/users/:id', (c) => {
  const id = c.req.param('id')
  return c.json({ userId: id })
})

// Multiple parameters
app.get('/posts/:postId/comments/:commentId', (c) => {
  const { postId, commentId } = c.req.param()
  return c.json({ postId, commentId })
})

// Optional parameters (using wildcards)
app.get('/files/*', (c) => {
  const path = c.req.param('*')
  return c.json({ filePath: path })
})

CRITICAL:

• c.req.param('name') returns single parameter
• c.req.param() returns all parameters as object
• Parameters are always strings (cast to number if needed)

Route Parameter Regex Constraints

Use regex patterns in routes to restrict parameter matching at the routing level:

// Only matches numeric IDs
app.get('/users/:id{[0-9]+}', (c) => {
  const id = c.req.param('id') // Guaranteed to be digits
  return c.json({ userId: id })
})

// Only matches UUIDs
app.get('/posts/:id{[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}}', (c) => {
  const id = c.req.param('id') // Guaranteed to be UUID format
  return c.json({ postId: id })
})

Benefits:

• Early validation at routing level
• Prevents invalid requests from reaching handlers
• Self-documenting route constraints

Query Parameters

app.get('/search', (c) => {
  // Single query param
  const q = c.req.query('q')

  // Multiple query params
  const { page, limit } = c.req.query()

  // Query param array (e.g., ?tag=js&tag=ts)
  const tags = c.req.queries('tag')

  return c.json({ q, page, limit, tags })
})

Best Practice:

• Use validation for query params (see Part 4)
• Provide defaults for optional params
• Parse numbers/booleans from query strings

Route Grouping (Sub-apps)

// Create sub-app
const api = new Hono()

api.get('/users', (c) => c.json({ users: [] }))
api.get('/posts', (c) => c.json({ posts: [] }))

// Mount sub-app
const app = new Hono()
app.route('/api', api)

// Result: /api/users, /api/posts

Why Group Routes:

• Organize large applications
• Share middleware for specific routes
• Better code structure and maintainability

---

Part 2: Middleware & Validation

CRITICAL Middleware Rule:

• Always call await next() in middleware to continue the chain
• Return early (without calling next()) to prevent handler execution
• Check c.error AFTER next() for error handling

app.use('/admin/*', async (c, next) => {
  const token = c.req.header('Authorization')
  if (!token) return c.json({ error: 'Unauthorized' }, 401)
  await next() // Required!
})

Built-in Middleware

import { Hono } from 'hono'
import { logger } from 'hono/logger'
import { cors } from 'hono/cors'
import { prettyJSON } from 'hono/pretty-json'
import { compress } from 'hono/compress'
import { cache } from 'hono/cache'

const app = new Hono()

// Request logging
app.use('*', logger())

// CORS
app.use('/api/*', cors({
  origin: 'https://example.com',
  allowMethods: ['GET', 'POST', 'PUT', 'DELETE'],
  allowHeaders: ['Content-Type', 'Authorization'],
}))

// Pretty JSON (dev only)
app.use('*', prettyJSON())

// Compression (gzip/deflate)
app.use('*', compress())

// Cache responses
app.use(
  '/static/*',
  cache({
    cacheName: 'my-app',
    cacheControl: 'max-age=3600',
  })
)

Custom Cache Middleware Pattern:

When implementing custom cache middleware for Node.js (or other non-Cloudflare runtimes), you must clone responses before storing them in cache:

const cache = new Map<string, Response>()

const customCache = async (c, next) => {
  const key = c.req.url

  // Check cache
  const cached = cache.get(key)
  if (cached) {
    return cached.clone() // Clone when returning from cache
  }

  // Execute handler
  await next()

  // Store in cache (must clone!)
  cache.set(key, c.res.clone()) // ✅ Clone before storing
}

app.use('*', customCache)

Why Cloning is Required: Response bodies are readable streams that can only be consumed once. Cloning creates a new response with a fresh stream.

**Built-in Middleware Reference**: See `references/middleware-catalog.md`

#### Streaming Helpers (SSE, AI Responses)

```typescript
import { Hono } from 'hono'
import { stream, streamText, streamSSE } from 'hono/streaming'

const app = new Hono()

// Binary streaming
app.get('/download', (c) => {
  return stream(c, async (stream) => {
    await stream.write(new Uint8Array([0x48, 0x65, 0x6c, 0x6c, 0x6f]))
    await stream.pipe(readableStream)
  })
})

// Text streaming (AI responses)
app.get('/ai', (c) => {
  return streamText(c, async (stream) => {
    for await (const chunk of aiResponse) {
      await stream.write(chunk)
      await stream.sleep(50) // Rate limit if needed
    }
  })
})

// Server-Sent Events (real-time updates)
app.get('/sse', (c) => {
  return streamSSE(c, async (stream) => {
    let id = 0
    while (true) {
      await stream.writeSSE({
        data: JSON.stringify({ time: Date.now() }),
        event: 'update',
        id: String(id++),
      })
      await stream.sleep(1000)
    }
  })
})

Use Cases:

• stream() - Binary files, video, audio
• streamText() - AI chat responses, typewriter effects
• streamSSE() - Real-time notifications, live feeds

WebSocket Helper

import { Hono } from 'hono'
import { upgradeWebSocket } from 'hono/cloudflare-workers' // Platform-specific!

const app = new Hono()

app.get('/ws', upgradeWebSocket((c) => ({
  onMessage(event, ws) {
    console.log(`Message: ${event.data}`)
    ws.send(`Echo: ${event.data}`)
  },
  onClose: () => console.log('Closed'),
  onError: (event) => console.error('Error:', event),
  // onOpen is NOT supported on Cloudflare Workers!
})))

export default app

⚠️ Cloudflare Workers WebSocket Caveats:

• Import from hono/cloudflare-workers (not hono/ws)
• onOpen callback is NOT supported (Cloudflare limitation)
• CORS/header-modifying middleware conflicts with WebSocket routes
• Use route grouping to exclude WebSocket routes from CORS:

const api = new Hono()
api.use('*', cors()) // CORS for API only
app.route('/api', api)
app.get('/ws', upgradeWebSocket(...)) // No CORS on WebSocket

Security Middleware

import { Hono } from 'hono'
import { secureHeaders } from 'hono/secure-headers'
import { csrf } from 'hono/csrf'

const app = new Hono()

// Security headers (X-Frame-Options, CSP, HSTS, etc.)
app.use('*', secureHeaders({
  xFrameOptions: 'DENY',
  xXssProtection: '1; mode=block',
  contentSecurityPolicy: {
    defaultSrc: ["'self'"],
    scriptSrc: ["'self'", "'unsafe-inline'"],
  },
}))

// CSRF protection (validates Origin header)
app.use('/api/*', csrf({
  origin: ['https://example.com', 'https://admin.example.com'],
}))

Security Middleware Options:

Middleware	Purpose
secureHeaders	X-Frame-Options, CSP, HSTS, XSS protection
csrf	CSRF via Origin/Sec-Fetch-Site validation
bearerAuth	Bearer token authentication
basicAuth	HTTP Basic authentication
ipRestriction	IP allowlist/blocklist

Combine Middleware

Compose middleware with conditional logic:

import { Hono } from 'hono'
import { some, every, except } from 'hono/combine'
import { bearerAuth } from 'hono/bearer-auth'
import { ipRestriction } from 'hono/ip-restriction'

const app = new Hono()

// some: ANY middleware must pass (OR logic)
app.use('/admin/*', some(
  bearerAuth({ token: 'admin-token' }),
  ipRestriction({ allowList: ['10.0.0.0/8'] }),
))

// every: ALL middleware must pass (AND logic)
app.use('/secure/*', every(
  bearerAuth({ token: 'secret' }),
  ipRestriction({ allowList: ['192.168.1.0/24'] }),
))

// except: Skip middleware for certain paths
app.use('*', except(
  ['/health', '/metrics'],
  logger(),
))

---

Part 3: Type-Safe Context Extension

Using c.set() and c.get()

import { Hono } from 'hono'

type Bindings = {
  DATABASE_URL: string
}

type Variables = {
  user: {
    id: number
    name: string
  }
  requestId: string
}

const app = new Hono<{ Bindings: Bindings; Variables: Variables }>()

// Middleware sets variables
app.use('*', async (c, next) => {
  c.set('requestId', crypto.randomUUID())
  await next()
})

app.use('/api/*', async (c, next) => {
  c.set('user', { id: 1, name: 'Alice' })
  await next()
})

// Route accesses variables
app.get('/api/profile', (c) => {
  const user = c.get('user') // Type-safe!
  const requestId = c.get('requestId') // Type-safe!

  return c.json({ user, requestId })
})

CRITICAL:

• Define Variables type for type-safe c.get()
• Define Bindings type for environment variables (Cloudflare Workers)
• c.set() in middleware, c.get() in handlers

Custom Context Extension

import { Hono } from 'hono'
import type { Context } from 'hono'

type Env = {
  Variables: {
    logger: {
      info: (message: string) => void
      error: (message: string) => void
    }
  }
}

const app = new Hono<Env>()

// Create logger middleware
app.use('*', async (c, next) => {
  const logger = {
    info: (msg: string) => console.log(`[INFO] ${msg}`),
    error: (msg: string) => console.error(`[ERROR] ${msg}`),
  }

  c.set('logger', logger)
  await next()
})

app.get('/', (c) => {
  const logger = c.get('logger')
  logger.info('Hello from route')

  return c.json({ message: 'Hello' })
})

Advanced Pattern: See templates/context-extension.ts

---

Part 4: Request Validation

Validation with Zod

npm install zod@4.3.5 @hono/zod-validator@0.7.6

import { zValidator } from '@hono/zod-validator'
import { z } from 'zod'

// Define schema
const userSchema = z.object({
  name: z.string().min(1).max(100),
  email: z.string().email(),
  age: z.number().int().min(18).optional(),
})

// Validate JSON body
app.post('/users', zValidator('json', userSchema), (c) => {
  const data = c.req.valid('json') // Type-safe!
  return c.json({ success: true, data })
})

// Validate query params
const searchSchema = z.object({
  q: z.string(),
  page: z.string().transform((val) => parseInt(val, 10)),
  limit: z.string().transform((val) => parseInt(val, 10)).optional(),
})

app.get('/search', zValidator('query', searchSchema), (c) => {
  const { q, page, limit } = c.req.valid('query')
  return c.json({ q, page, limit })
})

// Validate route params
const idSchema = z.object({
  id: z.string().uuid(),
})

app.get('/users/:id', zValidator('param', idSchema), (c) => {
  const { id } = c.req.valid('param')
  return c.json({ userId: id })
})

// Validate headers
const headerSchema = z.object({
  'authorization': z.string().startsWith('Bearer '),
  'content-type': z.string(),
})

app.post('/auth', zValidator('header', headerSchema), (c) => {
  const headers = c.req.valid('header')
  return c.json({ authenticated: true })
})

CRITICAL:

• Always use c.req.valid() after validation (type-safe)
• Validation targets: json, query, param, header, form, cookie
• Use z.transform() to convert strings to numbers/dates
• Validation errors return 400 automatically

⚠️ CRITICAL: Validation Must Be Handler-Specific

For validated types to be inferred correctly, validation middleware must be added in the handler, not via app.use():

// ❌ WRONG - Type inference breaks
app.use('/users', zValidator('json', userSchema))

app.post('/users', (c) => {
  const data = c.req.valid('json') // TS Error: Type 'never'
  return c.json({ data })
})

// ✅ CORRECT - Validation in handler
app.post('/users', zValidator('json', userSchema), (c) => {
  const data = c.req.valid('json') // Type-safe!
  return c.json({ data })
})

Why It Happens: Hono's Input type mapping merges validation results using generics. When validators are applied via app.use(), the type system cannot track which routes have which validation schemas, causing the Input generic to collapse to never.

Custom Validation Hooks

import { zValidator } from '@hono/zod-validator'
import { HTTPException } from 'hono/http-exception'

const schema = z.object({
  name: z.string(),
  age: z.number(),
})

// Custom error handler
app.post(
  '/users',
  zValidator('json', schema, (result, c) => {
    if (!result.success) {
      // Custom error response
      return c.json(
        {
          error: 'Validation failed',
          issues: result.error.issues,
        },
        400
      )
    }
  }),
  (c) => {
    const data = c.req.valid('json')
    return c.json({ success: true, data })
  }
)

// Throw HTTPException
app.post(
  '/users',
  zValidator('json', schema, (result, c) => {
    if (!result.success) {
      throw new HTTPException(400, { cause: result.error })
    }
  }),
  (c) => {
    const data = c.req.valid('json')
    return c.json({ success: true, data })
  }
)

Note on Zod Optional Enums: Prior to @hono/zod-validator@0.7.6, optional enums incorrectly resolved to strings instead of the enum type. This was fixed in v0.7.6. Ensure you're using the latest version:

npm install @hono/zod-validator@0.7.6

Validation with Valibot

npm install valibot@1.2.0 @hono/valibot-validator@0.6.1

import { vValidator } from '@hono/valibot-validator'
import * as v from 'valibot'

const schema = v.object({
  name: v.string(),
  age: v.number(),
})

app.post('/users', vValidator('json', schema), (c) => {
  const data = c.req.valid('json')
  return c.json({ success: true, data })
})

Zod vs Valibot: See references/validation-libraries.md

Validation with Typia

npm install typia @hono/typia-validator@0.1.2

import { typiaValidator } from '@hono/typia-validator'
import typia from 'typia'

interface User {
  name: string
  age: number
}

const validate = typia.createValidate<User>()

app.post('/users', typiaValidator('json', validate), (c) => {
  const data = c.req.valid('json')
  return c.json({ success: true, data })
})

Why Typia:

• Fastest validation (compile-time)
• No runtime schema definition
• AOT (Ahead-of-Time) compilation

Validation with ArkType

npm install arktype @hono/arktype-validator@2.0.1

import { arktypeValidator } from '@hono/arktype-validator'
import { type } from 'arktype'

const schema = type({
  name: 'string',
  age: 'number',
})

app.post('/users', arktypeValidator('json', schema), (c) => {
  const data = c.req.valid('json')
  return c.json({ success: true, data })
})

Comparison: See references/validation-libraries.md for detailed comparison

---

Part 5: Typed Routes (RPC)

Why RPC?

Hono's RPC feature allows type-safe client/server communication without manual API type definitions. The client infers types directly from the server routes.

Server-Side Setup

// app.ts
import { Hono } from 'hono'
import { zValidator } from '@hono/zod-validator'
import { z } from 'zod'

const app = new Hono()

const schema = z.object({
  name: z.string(),
  age: z.number(),
})

// Define route and export type
const route = app.post(
  '/users',
  zValidator('json', schema),
  (c) => {
    const data = c.req.valid('json')
    return c.json({ success: true, data }, 201)
  }
)

// Export app type for RPC client
export type AppType = typeof route

// OR export entire app
// export type AppType = typeof app

export default app

CRITICAL:

• Must use const route = app.get(...) for RPC type inference
• Export typeof route or typeof app
• Don't use anonymous route definitions

Client-Side Setup

// client.ts
import { hc } from 'hono/client'
import type { AppType } from './app'

const client = hc<AppType>('http://localhost:8787')

// Type-safe API call
const res = await client.users.$post({
  json: {
    name: 'Alice',
    age: 30,
  },
})

// Response is typed!
const data = await res.json() // { success: boolean, data: { name: string, age: number } }

Why RPC:

• ✅ Full type inference (request + response)
• ✅ No manual type definitions
• ✅ Compile-time error checking
• ✅ Auto-complete in IDE

⚠️ RPC Type Inference Limitation: The RPC client only infers types for json and text responses. If an endpoint returns multiple response types (e.g., JSON and binary), none of the responses will be type-inferred:

// ❌ Type inference fails - mixes JSON and binary
app.post('/upload', async (c) => {
  const body = await c.req.body() // Binary response
  if (error) {
    return c.json({ error: 'Bad request' }, 400) // JSON response
  }
  return c.json({ success: true })
})

// ✅ Separate endpoints by response type
app.post('/upload', async (c) => {
  return c.json({ success: true }) // Only JSON - types work
})

app.get('/download/:id', async (c) => {
  return c.body(binaryData) // Only binary - separate endpoint
})

RPC with Multiple Routes

// Server
const app = new Hono()

const getUsers = app.get('/users', (c) => {
  return c.json({ users: [] })
})

const createUser = app.post(
  '/users',
  zValidator('json', userSchema),
  (c) => {
    const data = c.req.valid('json')
    return c.json({ success: true, data }, 201)
  }
)

const getUser = app.get('/users/:id', (c) => {
  const id = c.req.param('id')
  return c.json({ id, name: 'Alice' })
})

// Export combined type
export type AppType = typeof getUsers | typeof createUser | typeof getUser

// Client
const client = hc<AppType>('http://localhost:8787')

// GET /users
const usersRes = await client.users.$get()

// POST /users
const createRes = await client.users.$post({
  json: { name: 'Alice', age: 30 },
})

// GET /users/:id
const userRes = await client.users[':id'].$get({
  param: { id: '123' },
})

RPC Performance Optimization

Problem: Large apps with many routes cause slow type inference

Solution: Export specific route groups instead of entire app

// ❌ Slow: Export entire app
export type AppType = typeof app

// ✅ Fast: Export specific routes
const userRoutes = app.get('/users', ...).post('/users', ...)
export type UserRoutes = typeof userRoutes

const postRoutes = app.get('/posts', ...).post('/posts', ...)
export type PostRoutes = typeof postRoutes

// Client imports specific routes
import type { UserRoutes } from './app'
const userClient = hc<UserRoutes>('http://localhost:8787')

Deep Dive: See references/rpc-guide.md

---

Part 6: Error Handling

HTTPException

import { Hono } from 'hono'
import { HTTPException } from 'hono/http-exception'

const app = new Hono()

app.get('/users/:id', (c) => {
  const id = c.req.param('id')

  // Throw HTTPException for client errors
  if (!id) {
    throw new HTTPException(400, { message: 'ID is required' })
  }

  // With custom response
  if (id === 'invalid') {
    const res = new Response('Custom error body', { status: 400 })
    throw new HTTPException(400, { res })
  }

  return c.json({ id })
})

CRITICAL:

• Use HTTPException for expected errors (400, 401, 403, 404)
• Don't use for unexpected errors (500) - use onError instead
• HTTPException stops execution immediately

Global Error Handler (onError)

import { Hono } from 'hono'
import { HTTPException } from 'hono/http-exception'

const app = new Hono()

// Custom error handler
app.onError((err, c) => {
  // Handle HTTPException
  if (err instanceof HTTPException) {
    return err.getResponse()
  }

  // Handle unexpected errors
  console.error('Unexpected error:', err)

  return c.json(
    {
      error: 'Internal Server Error',
      message: err.message,
    },
    500
  )
})

app.get('/error', (c) => {
  throw new Error('Something went wrong!')
})

Why onError:

• Centralized error handling
• Consistent error responses
• Error logging and tracking

Middleware Error Checking

app.use('*', async (c, next) => {
  await next()

  // Check for errors after handler
  if (c.error) {
    console.error('Error in route:', c.error)
    // Send to error tracking service
  }
})

Not Found Handler

app.notFound((c) => {
  return c.json({ error: 'Not Found' }, 404)
})

---

Critical Rules

Always Do

✅ Call await next() in middleware - Required for middleware chain execution ✅ Return Response from handlers - Use c.json(), c.text(), c.html() ✅ Use c.req.valid() after validation - Type-safe validated data ✅ Export route types for RPC - export type AppType = typeof route ✅ Throw HTTPException for client errors - 400, 401, 403, 404 errors ✅ Use onError for global error handling - Centralized error responses ✅ Define Variables type for c.set/c.get - Type-safe context variables ✅ Use const route = app.get(...) - Required for RPC type inference

Never Do

❌ Forget await next() in middleware - Breaks middleware chain ❌ Use res.send() like Express - Not compatible with Hono ❌ Access request data without validation - Use validators for type safety ❌ Export entire app for large RPC - Slow type inference, export specific routes ❌ Use plain throw new Error() - Use HTTPException instead ❌ Skip onError handler - Leads to inconsistent error responses ❌ Use c.set/c.get without Variables type - Loses type safety

---

Known Issues Prevention

This skill prevents 10 documented issues:

Issue #1: RPC Type Inference Slow

Error: IDE becomes slow with many routes (8-minute CI builds, non-existent IntelliSense) Source: hono/docs/guides/rpc | GitHub Issue #3869 Why It Happens: Complex type instantiation from typeof app with many routes. Exacerbated by Zod methods like omit, extend, pick. Prevention: Export specific route groups instead of entire app

// ❌ Slow
export type AppType = typeof app

// ✅ Fast
const userRoutes = app.get(...).post(...)
export type UserRoutes = typeof userRoutes

Advanced Workaround for Large Apps (100+ routes):

1. Split into monorepo libs:

// routers-auth/index.ts
export const authRouter = new Hono()
  .get('/login', ...)
  .post('/login', ...)

// routers-orders/index.ts
export const orderRouter = new Hono()
  .get('/orders', ...)
  .post('/orders', ...)

// routers-main/index.ts
const app = new Hono()
  .route('/auth', authRouter)
  .route('/orders', orderRouter)

export type AppType = typeof app

2. Use separate build configs:

   • Production: Full tsc with .d.ts generation (for RPC client)
   • Development: Skip tsc on main router, only type-check sub-routers (faster live-reload)

3. Avoid Zod methods that hurt performance:

   • z.omit(), z.extend(), z.pick() - These increase language server workload by 10x
   • Use interfaces instead of intersections when possible

Issue #2: Middleware Response Not Typed in RPC

Error: Middleware responses (including notFound() and onError()) not inferred by RPC client Source: honojs/hono#2719 | GitHub Issue #4600 Why It Happens: RPC mode doesn't infer middleware responses by default. Responses from notFound() or onError() handlers are not included in type map. Prevention: Export specific route types that include middleware

const route = app.get(
  '/data',
  myMiddleware,
  (c) => c.json({ data: 'value' })
)
export type AppType = typeof route

Specific Issue: notFound/onError Not Typed:

// Server
const app = new Hono()
  .notFound((c) => c.json({ error: 'Not Found' }, 404))
  .get('/users/:id', async (c) => {
    const user = await getUser(c.req.param('id'))
    if (!user) {
      return c.notFound() // Type not exported to RPC client
    }
    return c.json({ user })
  })

// Client
const client = hc<typeof app>('http://localhost:8787')
const res = await client.users[':id'].$get({ param: { id: '123' } })

if (res.status === 404) {
  const error = await res.json() // Type is 'any', not { error: string }
}

Partial Workaround (v4.11.0+): Use module augmentation to customize NotFoundResponse type:

import { Hono, TypedResponse } from 'hono'

declare module 'hono' {
  interface NotFoundResponse
    extends Response,
      TypedResponse<{ error: string }, 404, 'json'> {}
}

Issue #3: Validation Hook Confusion

Error: Different validator libraries have different hook patterns Source: Context7 research Why It Happens: Each validator (@hono/zod-validator, @hono/valibot-validator, etc.) has slightly different APIs Prevention: This skill provides consistent patterns for all validators

Issue #4: HTTPException Misuse

Error: Throwing plain Error instead of HTTPException Source: Official docs Why It Happens: Developers familiar with Express use throw new Error() Prevention: Always use HTTPException for client errors (400-499)

// ❌ Wrong
throw new Error('Unauthorized')

// ✅ Correct
throw new HTTPException(401, { message: 'Unauthorized' })

Issue #5: Context Type Safety Lost

Error: c.set() and c.get() without type inference Source: Official docs Why It Happens: Not defining Variables type in Hono generic Prevention: Always define Variables type

type Variables = {
  user: { id: number; name: string }
}

const app = new Hono<{ Variables: Variables }>()

Issue #6: Missing Error Check After Middleware

Error: Errors in handlers not caught Source: Official docs Why It Happens: Not checking c.error after await next() Prevention: Check c.error in middleware

app.use('*', async (c, next) => {
  await next()
  if (c.error) {
    console.error('Error:', c.error)
  }
})

Issue #7: Direct Request Access Without Validation

Error: Accessing c.req.param() or c.req.query() without validation Source: Best practices Why It Happens: Developers skip validation for speed Prevention: Always use validators and c.req.valid()

// ❌ Wrong
const id = c.req.param('id') // string, no validation

// ✅ Correct
app.get('/users/:id', zValidator('param', idSchema), (c) => {
  const { id } = c.req.valid('param') // validated UUID
})

Issue #8: Incorrect Middleware Order

Error: Middleware executing in wrong order Source: Official docs Why It Happens: Misunderstanding middleware chain execution Prevention: Remember middleware runs top-to-bottom, await next() runs handler, then bottom-to-top

app.use('*', async (c, next) => {
  console.log('1: Before handler')
  await next()
  console.log('4: After handler')
})

app.use('*', async (c, next) => {
  console.log('2: Before handler')
  await next()
  console.log('3: After handler')
})

app.get('/', (c) => {
  console.log('Handler')
  return c.json({})
})

// Output: 1, 2, Handler, 3, 4

Issue #9: JWT verify() Requires Algorithm Parameter (v4.11.4+)

Error: TypeError: Cannot read properties of undefined Source: GitHub Issue #4625 | Security Advisory GHSA-f67f-6cw9-8mq4 Why It Happens: Security fix in v4.11.4 requires explicit algorithm specification to prevent JWT header manipulation Prevention: Always specify the algorithm parameter

import { verify } from 'hono/jwt'

// ❌ Wrong (pre-v4.11.4 syntax)
const payload = await verify(token, secret)

// ✅ Correct (v4.11.4+)
const payload = await verify(token, secret, 'HS256') // Algorithm required

Note: This was a breaking change released in a patch version due to security severity. Update all JWT verification code when upgrading to v4.11.4+.

Issue #10: Request Body Consumed by Middleware

Error: TypeError: Body is unusable Source: GitHub Issue #4259 Why It Happens: Using c.req.raw.clone() bypasses Hono's cache and consumes the body stream Prevention: Always use c.req.text() or c.req.json() instead of accessing raw request

// ❌ Wrong - Breaks downstream validators
app.use('*', async (c, next) => {
  const body = await c.req.raw.clone().text() // Consumes body!
  console.log('Request body:', body)
  await next()
})

app.post('/', zValidator('json', schema), async (c) => {
  const data = c.req.valid('json') // Error: Body is unusable
  return c.json({ data })
})

// ✅ Correct - Uses cached content
app.use('*', async (c, next) => {
  const body = await c.req.text() // Cache-friendly
  console.log('Request body:', body)
  await next()
})

app.post('/', zValidator('json', schema), async (c) => {
  const data = c.req.valid('json') // Works!
  return c.json({ data })
})

Why: Request bodies in Web APIs can only be read once (they're streams). Hono's validator internally uses await c.req.json() which caches the content. If you use c.req.raw.clone().json(), it bypasses the cache and consumes the body, causing subsequent reads to fail.

---

Configuration Files Reference

package.json (Full Example)

{
  "name": "hono-app",
  "version": "1.0.0",
  "type": "module",
  "scripts": {
    "dev": "tsx watch src/index.ts",
    "build": "tsc",
    "start": "node dist/index.js"
  },
  "dependencies": {
    "hono": "^4.11.4"
  },
  "devDependencies": {
    "typescript": "^5.9.0",
    "tsx": "^4.19.0",
    "@types/node": "^22.10.0"
  }
}

package.json with Validation (Zod)

{
  "dependencies": {
    "hono": "^4.11.4",
    "zod": "^4.3.5",
    "@hono/zod-validator": "^0.7.6"
  }
}

package.json with Validation (Valibot)

{
  "dependencies": {
    "hono": "^4.11.4",
    "valibot": "^1.2.0",
    "@hono/valibot-validator": "^0.6.1"
  }
}

package.json with All Validators

{
  "dependencies": {
    "hono": "^4.11.4",
    "zod": "^4.3.5",
    "valibot": "^1.2.0",
    "@hono/zod-validator": "^0.7.6",
    "@hono/valibot-validator": "^0.6.1",
    "@hono/typia-validator": "^0.1.2",
    "@hono/arktype-validator": "^2.0.1"
  }
}

tsconfig.json

{
  "compilerOptions": {
    "target": "ES2022",
    "module": "ES2022",
    "lib": ["ES2022"],
    "moduleResolution": "bundler",
    "resolveJsonModule": true,
    "allowJs": true,
    "checkJs": false,
    "strict": true,
    "esModuleInterop": true,
    "skipLibCheck": true,
    "forceConsistentCasingInFileNames": true,
    "isolatedModules": true,
    "outDir": "./dist"
  },
  "include": ["src/**/*"],
  "exclude": ["node_modules"]
}

---

File Templates

All templates are available in the templates/ directory:

• routing-patterns.ts - Route params, query params, wildcards, grouping
• middleware-composition.ts - Middleware chaining, built-in middleware
• validation-zod.ts - Zod validation with custom hooks
• validation-valibot.ts - Valibot validation
• rpc-pattern.ts - Type-safe RPC client/server
• error-handling.ts - HTTPException, onError, custom errors
• context-extension.ts - c.set/c.get, custom context types
• package.json - All dependencies

Copy these files to your project and customize as needed.

---

Reference Documentation

For deeper understanding, see:

• middleware-catalog.md - Complete built-in Hono middleware reference
• validation-libraries.md - Zod vs Valibot vs Typia vs ArkType comparison
• rpc-guide.md - RPC pattern deep dive, performance optimization
• top-errors.md - Common Hono errors with solutions

---

Official Documentation

• Hono: https://hono.dev
• Hono Routing: https://hono.dev/docs/api/routing
• Hono Middleware: https://hono.dev/docs/guides/middleware
• Hono Validation: https://hono.dev/docs/guides/validation
• Hono RPC: https://hono.dev/docs/guides/rpc
• Hono Context: https://hono.dev/docs/api/context
• Context7 Library ID: /llmstxt/hono_dev_llms-full_txt

---

Dependencies (Latest Verified 2026-01-20)

{
  "dependencies": {
    "hono": "^4.11.4"
  },
  "optionalDependencies": {
    "zod": "^4.3.5",
    "valibot": "^1.2.0",
    "@hono/zod-validator": "^0.7.6",
    "@hono/valibot-validator": "^0.6.1",
    "@hono/typia-validator": "^0.1.2",
    "@hono/arktype-validator": "^2.0.1"
  },
  "devDependencies": {
    "typescript": "^5.9.0"
  }
}

---

Production Example

This skill is validated across multiple runtime environments:

• Cloudflare Workers: Routing, middleware, RPC patterns
• Deno: All validation libraries tested
• Bun: Performance benchmarks completed
• Node.js: Full test suite passing

All patterns in this skill have been validated in production.

---

Questions? Issues?

1. Check references/top-errors.md first
2. Verify all steps in the setup process
3. Ensure await next() is called in middleware
4. Ensure RPC routes use const route = app.get(...) pattern
5. Check official docs: https://hono.dev