The error messages must be clearer when you try to join a room

"I tried riot-dev, #riot-dev before I got it right, and it kept barking at me 'wrong format' without telling me what tye right format would look like.

And seems an obvious usability enhancement that it would either join your default home server or show you a list of rooms that kinda match what you mashed in"

(see https://matrix.to/#/!DdJkzRliezrwpNebLk:matrix.org/$1502179590731439dNUxo:matrix.org)

Reproduce the room-join flow with the reported inputs “riot-dev” and “#riot-dev”, then inspect where the “wrong format” message is generated. Use the linked Matrix discussion for context and define done as providing actionable format guidance; the requested default-server or room-matching behavior remains a separate scope question.

Written by the indexing model from the issue text.