My keyboard is repeating keys
A key that types itself over and over is either physically stuck or a repeat setting. One is a fault and the other is configuration.
A key that types itself repeatedly has two quite different causes, and one question separates them.
The question
Take your hands off the keyboard entirely and look at which keys register as held.
A key shows as held with nothing touching it. The switch is physically closed. This is a hardware fault.
Nothing shows as held, but keys repeat when you type. The switch is fine and your key repeat settings are too aggressive. This is configuration.
The distinction matters because the fixes have nothing in common.
If a key is stuck
Debris
The most common cause by a distance. Something under the keycap or inside the switch housing is holding the stem partially depressed.
Pull the keycap and look. Compressed air across the switch, then work the stem by hand a dozen times. On a mechanical board this resolves most cases.
A keycap that is not seated
A cap fitted at a slight angle, or one that has swollen from a cleaning, can hold the switch down. This is common right after cleaning a board, which is why the problem often appears immediately afterwards.
Liquid
A spill leaves residue that is sticky when dry, and sugary drinks are far worse than water. The residue holds contacts together. Isopropyl alcohol and patience, with the keyboard disconnected and fully dry before power.
A failed switch
If the switch is clean and still registers as held, it has failed shorted. On a hot-swap board, pull it and fit a spare. On a soldered board it is a desoldering job. On a membrane keyboard it is not economically repairable.
If it is the repeat settings
Every operating system has two values: the delay before repeating starts, and the rate once it does.
A delay set very short makes ordinary typing produce doubles, because a normal keypress lasts long enough to trigger the repeat. Lengthening the delay fixes it immediately.
Check accessibility settings too. Filter Keys on Windows and Slow Keys on macOS both change how held keys behave, and both are easy to enable accidentally with a keyboard shortcut.
If it is software
Anything sitting between the keyboard and the operating system can produce repeats: remapping utilities, macro software, text expanders, and gaming keyboard configuration apps.
Gaming keyboards are worth special attention because they store profiles in onboard memory, so a bad macro follows the keyboard to another computer. That makes it look like a hardware fault. Reset the keyboard to factory defaults through its software to rule this out.
Ruling out the keyboard entirely
Try the keyboard on a different computer. A fault that follows the keyboard is hardware. A fault that stays with the computer is settings or software, and no amount of cleaning will help.
If you are on a laptop, plug in an external keyboard and see whether it also repeats. If it does, the problem is the machine rather than either keyboard.
Common questions
How do I tell a stuck key from a repeat setting?
Take your hands off the keyboard and look at which keys register as held. A stuck key shows as held with nothing touching it. A repeat delay set too short shows nothing held, because the key is only repeating while you are actually pressing it.
Only one key repeats. Is the whole keyboard failing?
No. A single repeating key is almost always debris in that one switch or a worn contact in that one position. The rest of the board is unaffected, and on a hot-swap keyboard the fix is a thirty second switch change.
It started after cleaning the keyboard.
Liquid in the switch, or a keycap not fully seated. A cap sitting slightly proud holds the stem partially depressed. Pull the cap, let everything dry completely, and refit it firmly.
My laptop key repeats only sometimes.
Intermittent repeating on a laptop is usually debris under the scissor mechanism. Compressed air across the key at an angle resolves a good share of these. If it persists, the individual key mechanism can often be replaced on most laptops.
Could this be a software problem?
Yes. Remapping software, macro tools and text expanders all sit between the keyboard and the operating system and can produce repeats. Also check accessibility settings, since Filter Keys and similar features change how repeats behave.