Hono Routing & Middleware

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)

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](https://hono.dev/docs/guides/rpc) | [GitHub Issue #3869](https://github.com/honojs/hono/issues/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](https://github.com/honojs/hono/issues/2719) | [GitHub Issue #4600](https://github.com/honojs/hono/issues/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](https://github.com/honojs/hono/issues/4625) | [Security Advisory GHSA-f67f-6cw9-8mq4](https://github.com/honojs/hono/security/advisories/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](https://github.com/honojs/hono/issues/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