The easiest urban planter box to assemble with no tools is a fabric raised planter bed. It arrives as a single, pre-sewn piece: you unfold it, set it in place, and fill it with soil. There are no screws, bolts, panels, or confusing diagrams. For a renter on a balcony or someone gardening on a small patio, that zero-tool setup is hard to beat. Fabric beds are lightweight, store flat when empty, and are usually made from breathable geotextile fabric that helps prevent waterlogging and air-prunes roots. Choose a size that fits your space, place it on a level surface, and add a liner or drip tray if you are on a balcony. Then fill it with a good container mix and plant.
If you specifically want a rigid, box-shaped planter, choose a modular snap-together plastic planter. Look for push-fit panels, twist-lock corners, or click-in feet. Avoid wooden kits and metal raised beds that need bolts, nuts, and a wrench. Before buying, check that the parts are hand-assemblable, that drainage holes are included, and that the planter can hold enough soil without being too heavy for your balcony. A snap-together plastic box is still tool-free, but it usually takes a few minutes longer than a fabric bed.
For no-tool success, keep the planter near a water source, use lightweight potting mix, and leave space for drainage. If wind is strong, add weight or secure the planter. The best choice is the one you can actually set up today: a fabric raised bed for the absolute easiest assembly, or a snap-together plastic planter box if you want straight edges and a more traditional look.