Webhooks are used by Starling and Monzo to integrate with external services such as Sync for YNAB. They essentially send us a notification every time you spend money. We then use that data to push that transaction into YNAB.
They are much more secure than other connections because we have no access to your bank account at all, and all we can do is process the webhook. We cannot fetch historical data from your bank account, see any balances etc.