List the user’s Gmail labels. Returns both system labels (INBOX, SENT, DRAFTS, UNREAD, STARRED, TRASH, SPAM, IMPORTANT, CATEGORY_PERSONAL, CATEGORY_SOCIAL, CATEGORY_PROMOTIONS, CATEGORY_UPDATES, CATEGORY_FORUMS, etc.) and any custom user-created labels. Each label has a UUID id and a name. Gmail represents nearly every inbox operation as a label add/remove, so this tool is the first step for almost any thread-management action: call ListLabels once to find the label id by name, then pass that id to UpdateThreadLabels. Common pairings (look up the named system label here, then call UpdateThreadLabels with that id): - Archive a thread → remove INBOX (add=false) - Move back to inbox → add INBOX (add=true) - Mark as read → remove UNREAD (add=false) - Mark as unread → add UNREAD (add=true) - Star → add STARRED; Unstar → remove STARRED - Move to trash → add TRASH; Restore from trash → remove TRASH - Mark important → add IMPORTANT; Mark unimportant → remove IMPORTANT - Report spam → add SPAM; Not spam → remove SPAM - Apply or remove a custom user label → look up the label by its display name and add/remove it Match label names case-insensitively when searching the response. You can also use this to understand how the user’s mail is organized before filtering or searching by label. Labels are per-inbox: each inbox has its own label ids, so a label id from one inbox will not work on a thread in another. When acting on a specific thread, pass its thread_id and this returns the labels of the inbox that owns that thread (the matching ids to pass to UpdateThreadLabels). Otherwise, in a multi-inbox setup, pass inbox (an inbox email address from ListInboxes) to list a specific inbox’s labels; omit both to use the primary inbox.