This extension displays the number of unread emails from multiple Google accounts in the badge area of the toolbar button which is equivalent to "is:unread label:inbox" search query. The extension does not store user's credential information for privacy concerns instead uses Gmail active session to perform searches (for the extension to operate you need to be logged-in into at least one Gmail account). Since Gmail allows multiple account access, this extension is also capable to display the number of unread emails for all the logged-in accounts.
A user can define multiple search queries for each account from the options page and the badge number will be the total number of search items. When the toolbar button is clicked the most recent Gmail thread is opened (this action is configurable from the options page). To open other Gmail accounts, use the right-click context-menu items.
The extension supports all the official Gmail operators in the search queries hence you can define a complex search query and ask the extension to observe these queries.
This extension is useful for those who need a powerful Gmail notifier, not a Gmail client.