Why does my toaster brown one side of the bread more than the other?
Because toasting depends on radiant heat reaching the bread surface, and very little in a domestic toaster guarantees that both sides receive the same amount. Some of the causes are normal design behaviour and some indicate a fault worth acting on.
The most common normal cause is a single-slice load in a two-slice toaster. Each slot has heating elements on both sides, but the outer element and the central one shared between slots often deliver slightly different output, and with only one slice in, there is nothing absorbing heat on the other side of the central element. Many toasters have a single-slice setting specifically for this, and using the slot the manual recommends makes a visible difference.
The bread itself matters more than people expect. Uneven thickness, irregular density in artisan or home-baked loaves, and differences in moisture between the two faces all produce uneven browning. Bread straight from the freezer browns unevenly unless the defrost setting is used.
A genuine fault shows up as consistent unevenness with two slices in, on every cycle. The usual cause is a broken element — the wire on one side has failed, and that side only receives heat from the opposite element. Holding the lever down briefly in a dark kitchen and looking at whether both sides glow evenly is a quick diagnostic. Do not do this with anything metal, and unplug before investigating further.
A thick layer of crumbs in the tray also absorbs and reflects heat unevenly, and is worth clearing regularly for fire-safety reasons as much as for browning.
On an inexpensive toaster with a failed element, replacement is usually more economical than repair.