# Type Alias: RequestId

> 

> **RequestId**: `number` \| `string` \| `null`

Defined in: [packages/server/src/unstable-core-do-not-import/rpc/envelopes.ts:23](https://github.com/trpc/trpc/blob/57482b0bb09dce5c838dc8bf5727a943488bac61/packages/server/src/unstable-core-do-not-import/rpc/envelopes.ts#L23)