Only talk and no action; a derogatory expression for someone who just talks without following through (also said as 口ばっかり).
彼はいつも口ばかりで、約束を守らない。
He is all talk and never keeps his promises.
口ばっかり言ってないで、まず行動してみてください。
Stop just talking and try taking action first.
意見は立派だけど、口ばかりでは信頼されない。
Your ideas are fine, but if it's all talk you won't be trusted.