I love to shop online so I get lots of practice opening boxes. Several years ago I figured out a way to open most of these shipping boxes with just my hands.
The top of your typical shipping box has two flaps that fold down and meet in the middle. A piece of strapping tape covers the edges of the flaps from one end to the other and the tape folds over the ends of the box to hold the flaps down. Normally people cut the tape at the ends of the box, and then cut between the top flaps, so that they can free the flaps.
Instead, I stand the box on one end so the top flaps are on the side and one end of the tape is on the end facing up. I put my thumbs on that end of the box, one thumb on each side of the tape and press down. I push the end of the box in under the top flaps. The end of the box goes in just a bit and the tape is pulled away from side. I then put my fingers under the loosened tape and pull it up which usually frees that end of the tape. I then pull the tape along the top of the box to remove as much of it as I can. If the tape doesn’t come off enough to free the flaps, I flip the box so that the other end is on top and repeat these steps. Once most the tape is removed pushing in on the top flaps usually allows them to be pulled apart. I have even added a short YouTube video to illustrate the process.
This works best with plastic tape. It is a bit trickier with paper tape which is often reinforced with string. This type of tape often rips before you can pull it all the way across the top. But even then I can usually pull enough tape off to push in and separate the flaps.
BTW, this technique is also useful to release the bottom flaps when you want to break down the boxes for disposal.