Airbus Flight Attendant reported the gate agent began to open the cabin door from the outside without getting a thumbs up. There was no escape slide deployment but proper procedure was not followed.

Narrative

The Captain informed the flight attendants about a potential tail tip when we got to our gate. He stated we would leave seatbelt sign on and passengers seated while ground crew unloaded bags to help with the tail tip situation. The seatbelt sign stayed on and the doors were still armed. FA A (Flight Attendant) noticed the gate agent moving the jet bridge to door 1L. She said he did 2 knocks and didn't even check for thumbs up. She was on the other side indicating a no motion with her hands; telling him not to open. He started to open the door so she pushed down on the door operating handle while FA B; quickly disarmed door. There was no slide deployment but we informed gate agent he needed to wait for the thumbs up. We were flying the Airbus and there is a safety guard so it is supposed to disarm from the outside; but proper procedures we have in place to ensure no ISDs (Inadvertent Slide Deployments) are caused was not followed by the gate agent. Captain then turned the seatbelt sign off and Flight Attendant B made disarming announcement. I then disarmed my door (1R) and had Flight Attendant B cross check my door; but as hers was already opened I couldn't complete the proper cross check to her door. We informed captain about the situation.