Jumping spider enclosures are one of the simplest setups in the invertebrate hobby. You don't need heating equipment, UVB lights, misting systems, or any of the other kit that reptile keepers accumulate. You need a ventilated box, some stuff to climb on, and a way to get water droplets on the walls. That's genuinely it.
But "simple" doesn't mean "anything goes." The details matter, and getting a few things wrong can make the difference between a spider that thrives and one that struggles.
Size and shape
Jumping spiders are arboreal. They spend most of their time at the top of whatever space they're in, and they'll build their web sac (the silk retreat they sleep and moult in) at the highest available point. This means tall enclosures are better than wide ones. A container about 15-20cm on each side works for most adult specimens of commonly kept species like Phidippus regius.
Too large is actually a problem. In an oversized enclosure, a small spider can struggle to locate prey, and you'll struggle to locate the spider. Slings (spiderlings) should start in something much smaller, maybe a 5-8cm deli cup or similar, and move up as they grow. A container roughly three times the spider's legspan in each dimension is a reasonable guideline.
Purpose-built jumping spider enclosures are sold by several UK suppliers now. They're typically acrylic boxes with a hinged front door and mesh ventilation panels. They look nice on a shelf and they work well. But they're not necessary. A modified sweet jar, a repurposed sauce bottle, or a deli cup with holes melted in the lid all work perfectly. The spider doesn't care about aesthetics.
Ventilation
This is the most important design element. Stagnant air causes mould, and mould in a tiny enclosure creates unhealthy conditions quickly. Cross-ventilation (mesh or holes on two opposite sides) is best because it creates actual airflow rather than just a single opening where air barely moves.
If you're making your own enclosure, a soldering iron works well for melting ventilation holes in plastic. Cover larger openings with fine mesh (hot-glued in place) to prevent escapes. The mesh needs to be fine enough that the spider can't squeeze through. For slings, this means very fine mesh or fabric.
Magnetic mesh vents are another option. Some people cut a hole in the lid and attach a magnetic mesh cover that can be removed for feeding. It works, though I find a simple hinged door or removable lid just as practical.
Substrate
Jumping spiders don't interact with the substrate much. They live up high and only come down to the floor occasionally. A thin layer of something absorbent (coco fibre, paper towel, or sphagnum moss) on the bottom catches any moisture that drips down from misting and makes cleaning easy. That's all it needs to do.
Paper towel is the most practical option for maintenance. You can see at a glance if there are food remains or mould, and you can swap it out in seconds. Coco fibre and sphagnum look better and hold moisture longer, which can help with humidity in drier environments. Either approach works fine.
Climbing surfaces and decor
Give the spider things to climb on and places to anchor its web sac. Cork bark is popular and looks natural. Fake plants (the small silk or plastic ones sold for fish tanks or dollhouses) add visual complexity and give the spider surfaces to hunt from. A small stick or twig propped at an angle provides a highway between the floor and the top of the enclosure.
Don't overcrowd the space. A couple of items is enough. The spider needs room to jump and hunt, and you need to be able to see what's going on inside. If the enclosure is so packed with decor that you can't find the spider or its prey, you've overdone it.
Avoid anything with sharp edges that could snag on a moulting spider. Avoid materials treated with pesticides, varnish, or paint. Natural, untreated materials are safest. If you're collecting sticks or bark from outside, give them a quick rinse and let them dry first, mostly to remove any hitchhiking mites or tiny spiders that might already be in residence.
Lighting
Jumping spiders are diurnal visual hunters. They use their eyesight (those large anterior median eyes can resolve detail at surprising distances for animals their size) to locate and stalk prey. They need a light-dark cycle to maintain normal behaviour, so placing the enclosure in a room with natural light is the simplest approach.
Don't put the enclosure in direct sunlight. A small plastic or acrylic box in direct sun becomes an oven within minutes. Near a window but out of the sun's direct path is ideal. If the room where you keep the spider gets very little natural light, a nearby desk lamp on a timer provides enough to establish a day/night cycle.
Humidity and water
Jumping spiders drink from water droplets on enclosure walls and decor. Mist the inside of the enclosure lightly every 2-3 days with dechlorinated water or, more practically, just use a clean spray bottle with tap water that's been left to sit for 24 hours. Spray the walls, not the spider. Water droplets can trap small spiders, particularly slings.
You don't need a water dish. In fact, a water dish in a jumping spider enclosure is a drowning risk, especially for slings. The misting approach is safer and mimics how they'd encounter water in the wild (dew and rain on surfaces).
If you notice the web sac looks dry and papery, or the spider seems reluctant to leave it, you might need to mist slightly more often. If there's persistent condensation and the substrate is soggy, cut back. It's a balance, but it's not a difficult one to find.
Placement
Somewhere with stable temperature (18-24C suits most species), indirect natural light, and away from draughts and vibrations. Don't put the enclosure next to a speaker, on top of a washing machine, or in a spot where people constantly brush past it. Jumping spiders are sensitive to vibrations and will retreat into their web sacs if they feel threatened.
A shelf at roughly eye level is nice because you can observe the spider without bending down or reaching up, and the spider is at a height it's naturally comfortable with. A desk works too. Anywhere stable and quiet enough that the spider feels secure.