# MiddlewareFn

**Kind:** Type

**Source:** [`packages/platform-fastify/adapters/middie/fastify-middie.ts`](https://github.com/nestjs/nest/blob/master/packages/platform-fastify/adapters/middie/fastify-middie.ts#L17)

**Part of:** [Platform Fastify](subsystem-packages-platform-fastify)

## Definition

```ts
(req: Req, res: Res, next: (err?: unknown) => void) => void
```