What is N-key rollover (NKRO)?
N-key rollover means the keyboard can report every simultaneously pressed key independently, with no limit on the count. Keys are arranged in a grid (matrix) and cheap controllers can confuse certain combinations — pressing three corners of a rectangle can phantom-register a fourth. NKRO boards solve this with per-key diodes and a controller that scans each switch individually. Most NKRO keyboards must be in USB N-key mode (sometimes a Fn-toggle); some default to 6KRO for BIOS compatibility. DeviceCheckOnline lights every key the browser sees, so you can verify the true count live.
What is the difference between 6KRO and NKRO?
6KRO (6-key rollover) is the USB HID boot-protocol standard: the keyboard reports up to six non-modifier keys plus the eight modifiers (Ctrl, Shift, Alt, Meta on each side) at once. NKRO uses a custom HID report that encodes every key as a single bit in a bitfield, so there is no practical cap. For typing you will rarely exceed six keys, but for gaming — especially rhythm games, fighting games and WASD plus diagonals plus shift plus space — NKRO prevents missed inputs.
What is ghosting and how does this test reveal it?
Ghosting is when the keyboard reports a key you did not press, caused by the matrix topology: three keys forming an L can complete an electrical circuit through a fourth. Anti-ghosting circuitry (diodes per switch) blocks that phantom current. In DeviceCheckOnline, press three or four keys in a rectangle — common test combos are W+A+S, Q+W+E+R, or your gaming chord — and watch the live count. If a key you did not press lights up, the matrix is ghosting. If a real press fails to light, that is blocking, not ghosting.
Why does my keyboard only show 6 keys even though it advertises NKRO?
Almost certainly the board is in 6KRO mode. Many keyboards ship in 6KRO for BIOS and bootloader compatibility and require a firmware toggle — often Fn+N, Fn+K, or a setting in the manufacturer's software (Razer Synapse, Corsair iCUE, VIA, QMK config) — to switch to full NKRO. USB wireless dongles, KVM switches, and some USB hubs can also force the report back to 6KRO. Plug directly into a rear motherboard USB port and re-run the test.
Do I actually need NKRO?
For typing, no — humans rarely hold more than three or four keys at once, and 6KRO plus modifiers covers it. For gaming it depends on the genre. FPS players holding W+Shift+Space while pressing R to reload and Q to peek can hit the 6KRO ceiling; rhythm games (osu!mania, Stepmania), fighting games and flight sims regularly exceed it. If you encounter dropped inputs during specific combos, NKRO will help. Otherwise 6KRO is sufficient.
Why are some combos blocked even on NKRO boards?
A handful of combinations are blocked by the operating system or the browser before the report reaches the page. The classic example is Ctrl+Alt+Delete on Windows, which is a secure attention sequence. Browsers also reserve combos like Ctrl+T, Ctrl+W and F11. If a combo fails only in DeviceCheckOnline but works in a native app, suspect a browser-reserved shortcut. If it fails everywhere, run /keyboard/tester to check individual keys and /keyboard/chatter to rule out switch issues.