be all talk (and no action)

To talk a lot about something that one has not actually done or will not actually do. She may brag about donating money to the school, but I know she's all talk and no action. Oh, he's all talk—he's never worked a day in his life! John's all talk and no action, so I doubt he'll really help you move those boxes, like he said he would.

be all ˈtalk (and no action)

(disapproving) be a person who talks a lot about what they are going to do or have done without actually doing much: Don’t listen to her promises — she’s all talk and no action.