[API reference](https://evolu.dev/docs/api-reference) › [@evolu/common](https://evolu.dev/docs/api-reference/common) › [local‑first/Protocol](https://evolu.dev/docs/api-reference/common/local-first/Protocol) › parseProtocolHeader

```ts
function parseProtocolHeader(
  inputMessage: Uint8Array,
): Result<ProtocolHeader, ProtocolInvalidDataError>;
```

Defined in: [packages/common/src/local-first/Protocol.ts:370](https://github.com/evoluhq/evolu/blob/e7144e2bbe9069362b62dec1b64a8aa922b8f1b0/packages/common/src/local-first/Protocol.ts#L370)

Parses the protocol header needed for routing.

Every protocol message begins with `protocolVersion`, `ownerId`, and
`messageType`.