The interesting thing here is the permission model rather than the tool count: the connection acts within your workspace permissions rather than as a service identity, which is the design you want when the surface eventually grows to touch the warehouse. Take the trial before the add-on, and check what has shipped since — a single-tool endpoint on a data platform is a beginning, not a product.
Weld is a data platform. Their documented endpoint surface is currently minimal: a single tool listing accounts, operating inside the permissions your workspace already grants you.
List_accounts. Their walkthrough shows using it from an assistant against your workspace.
OAuth or an API key. It requires their premium plan or above, sold as a monthly add-on, with a two-week test available on the entry plan.
Paste a URL, then authorize — add the endpoint to your client, then approve the OAuth consent screen