# NotFoundResponse

**Kind:** Interface

**Source:** [`src/types.ts`](https://github.com/honojs/hono/blob/main/src/types.ts#L105)

You can extend this interface to define a custom `c.notFound()` Response type.

`NotFoundResponse` is a type extension point for the response returned by `c.notFound()`. Extend it through module augmentation to describe the JSON body your application returns for missing routes or resources.

## Diagram

```mermaid
graph LR
  A[Module augmentation] --> B[NotFoundResponse]
  B --> C[c.notFound()]
  C --> D[Typed not-found response]
```

## Usage

```ts
import { Hono } from 'hono'

declare module 'hono' {
  interface NotFoundResponse {
    error: 'NOT_FOUND'
    resource: string
  }
}

const app = new Hono()

app.notFound((c) => {
  return c.json(
    {
      error: 'NOT_FOUND',
      resource: c.req.path,
    },
    404
  )
})

app.get('/posts/:id', (c) => {
  const post = null

  if (!post) {
    return c.notFound()
  }

  return c.json(post)
})
```

## AI Coding Instructions

- Extend `NotFoundResponse` with module augmentation instead of replacing the interface.
- Keep fields declared on `NotFoundResponse` aligned with the object returned by the configured not-found handler.
- Return `c.notFound()` from routes that cannot locate a requested resource.
- Define a shared not-found handler with `app.notFound()` when the application needs a consistent response body.