Adding observers to boards
Teams that subscribe to Trello Business Class can add "Observers" to boards within their team. Observers are board members that are able to view a board and the cards within the board, download card attachments, comment and vote on cards if that is enabled for the board, and export the board.
Observers are not able to move or edit cards, upload card attachments, tick the box on a checklist item, and Observers can't change board settings.
Because an Observer is a board member permission and not a membership type, a Business Class board admin can set both team members and Guests as an Observer on a board. There are no limits to how many Observers you can have on a board, and an Observer can be a billable team member or Multi-Board Guest or a non-billable Single-Board Guest. To understand if an Observer is billable, check out the page How Billing Works with Trello Business Class.
Add an observer
To add someone to your board as an Observer, click "Invite" from the top of the board. Enter the member's username or email address. When you choose the person to add, the default choice is to add them as regular board members, but you can click on the down arrow to change that to "Add as Observers."
Because an Observer is a board member permission it isn't currently possible to set a user as an Observer at the team level, and each Observer is set individually per member per board.
Change a member's permissions to Observer
To change a current board member's permissions to Observer, click their avatar from the Members section of the board menu, select "Change Permissions" and select "Observer". Please note that only team admins and board admins can change a board member's permissions.
Change a board member's permissions to Observer.