# requestId

**Kind:** Function

**Source:** [`src/middleware/request-id/request-id.ts`](https://github.com/honojs/hono/blob/main/src/middleware/request-id/request-id.ts#L41)

**Part of:** [Middleware](subsystem-src-middleware)

Request ID Middleware for Hono.

`requestId` is Hono middleware that assigns an identifier to each incoming request. It makes the identifier available through the request context and returns it in the response header so logs, handlers, and clients can reference the same request.

## Signature

```ts
function requestId({
  limitLength = 255,
  headerName = 'X-Request-Id',
  generator = () => crypto.randomUUID(),
}: RequestIdOptions): MiddlewareHandler
```

## Parameters

| Name | Type |
|---|---|
| `{
  limitLength = 255,
  headerName = 'X-Request-Id',
  generator = () => crypto.randomUUID(),
}` | `RequestIdOptions` |

**Returns:** `MiddlewareHandler`

## Diagram

```mermaid
graph LR
  Client[Client Request] --> Middleware[requestId Middleware]
  Middleware --> Context[Hono Context: requestId]
  Middleware --> Handler[Route Handler]
  Handler --> Response[Response with Request ID Header]
```

## Usage

```ts
import { Hono } from 'hono'
import { requestId } from 'hono/request-id'

const app = new Hono()

app.use('*', requestId())

app.get('/status', (c) => {
  const id = c.get('requestId')

  return c.json({
    requestId: id,
    status: 'ok',
  })
})

export default app
```

## AI Coding Instructions

- Register `requestId()` before route handlers that need access to `c.get('requestId')`.
- Use the request ID when writing logs or reporting errors so related events can be correlated.
- Preserve the response request ID header when adding middleware that creates or replaces responses.
- Avoid generating separate request IDs inside handlers; read the value already stored on the Hono context.