The reason most people don't add storage to a tight seam is the dread of drilling — measuring twice, hitting a tile, patching a wall later. A slide-on gap shelf skips all of that, which is the whole reason it exists. If you can slide a book onto a shelf, you can install this. Here's what the job actually looks like.
What "slide-on" means
The slim gap shelf is shaped to clip into the seam between the fridge and the wall, or beside the washer. You don't screw it, you slide it into the gap until it sits. No level, no anchors, no power drill, no wander around the house looking for a bit. If the seam is about 5.9 inches, the shelf is built to seat there.
The five-minute version
Clear the bottles off the top of the appliance, slide the shelf into the seam, nudge it level with your hand, and load it with the daily-reach jars. That's it. Because there are no holes, nothing is permanent — when you rearrange the kitchen or move, it lifts back out and the wall and appliance look untouched. No patch, no paint, no arguing with a landlord about "improvements."
Why carbon steel and not plastic
A slide-on shelf carries jars and bottles, and plastic sags and stains under that load in a kitchen or laundry room. Carbon steel holds the row without bowing and wipes clean when a cap leaks. The shelf is thin but rated for the weight a real caddy carries, so a full row of detergents or oils won't bow it by month three.
Give your seam a job with a no-drill slim gap shelf, or see the narrow storage range.