> ## Documentation Index
> Fetch the complete documentation index at: https://mintlify.com/honojs/hono/llms.txt
> Use this file to discover all available pages before exploring further.

# logger

> API reference for the Logger middleware

## Import

```typescript theme={null}
import { logger } from 'hono/logger'
```

## Usage

```typescript theme={null}
const app = new Hono()

app.use(logger())

app.get('/', (c) => c.text('Hello Hono!'))
```

## Options

The `logger` middleware accepts an optional print function:

<ParamField path="fn" type="(str: string, ...rest: string[]) => void" default="console.log">
  Optional function for customized logging behavior. This function will be called with the formatted log message.
</ParamField>

## Signature

```typescript theme={null}
logger(fn?: PrintFunc): MiddlewareHandler
```

## Examples

### Basic usage

```typescript theme={null}
const app = new Hono()

app.use(logger())

app.get('/', (c) => c.text('Hello Hono!'))

// Logs:
// --> GET /
// <-- GET / 200 5ms
```

### Custom print function

```typescript theme={null}
import { logger } from 'hono/logger'

app.use(logger((message) => {
  console.log('Custom:', message)
}))
```

### Log to file

```typescript theme={null}
import fs from 'fs'

const logStream = fs.createWriteStream('app.log', { flags: 'a' })

app.use(logger((message) => {
  logStream.write(message + '\n')
}))
```

### Structured logging

```typescript theme={null}
app.use(logger((message) => {
  const logEntry = {
    timestamp: new Date().toISOString(),
    message,
  }
  console.log(JSON.stringify(logEntry))
}))
```

### Conditional logging

```typescript theme={null}
const isDevelopment = process.env.NODE_ENV === 'development'

if (isDevelopment) {
  app.use(logger())
}
```

### Apply to specific routes

```typescript theme={null}
const app = new Hono()

// Only log API routes
app.use('/api/*', logger())

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

## Output Format

The logger produces two lines per request:

1. **Incoming request**: `--> METHOD PATH`
2. **Outgoing response**: `<-- METHOD PATH STATUS DURATION`

### Examples

```
--> GET /api/users
<-- GET /api/users 200 12ms

--> POST /api/users
<-- POST /api/users 201 45ms

--> GET /not-found
<-- GET /not-found 404 3ms
```

### Status Code Colors

When color is enabled (supported terminal), status codes are color-coded:

* **2xx** (Success): Green
* **3xx** (Redirect): Cyan
* **4xx** (Client Error): Yellow
* **5xx** (Server Error): Red

## Behavior

* Logs incoming request before handler execution
* Logs outgoing response after handler completes
* Includes response status code and elapsed time
* Time is displayed in milliseconds for durations \< 1 second
* Time is displayed in seconds (rounded) for durations >= 1 second
* Automatically detects color support in terminal
* Works with all HTTP methods
* Extracts path from full URL for cleaner logs