> ## Documentation Index
> Fetch the complete documentation index at: https://www.plain.com/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# threadByExternalId

> Fetch a thread by the external ID you assigned it, scoped to a specific customer. Because `externalId` is only unique per-customer, both `customerId` and `externalId` are required. Returns null if no match. Requires the `thread:read` permission.