N-Key Rollover Test With Gaming Key Combinations

Click the test area, then hold down keys to see how many your keyboard reports at once.

0 keys held

Most at once: 0

Click here or press Start, then hold down any keys.

Together: 0 of 6. Still dark: W, A, S, D, Left Shift, Space.

  • W
  • A
  • S
  • D
  • Left Shift
  • Space

Press Esc to leave the test. Leave Ctrl out. Ctrl with W closes the tab in most browsers before a page can stop it.

More options

Your last five runs

  1. No run yet.

Nothing from this test is stored unless you tick the box. Kept runs are numbers only and never leave this browser.

How this check works

W, A, S, D, Left Shift and Space

Move, sprint and jump at once, the left-hand chord of a first-person game. Shift travels in the modifier byte of a USB report, so this uses five of the six key-code slots. A key that stays dark here points to the key matrix and not to the USB limit.

The page counts the keys your browser says are down. A laptop Fn key never reaches a web page.

  • The page keeps a list of the keys that are down, by their position on the board, and counts the list.
  • The most that were ever down together is kept until you start over, along with the best count for the combination you chose.
  • When the window loses focus the list is emptied, because a key released elsewhere would otherwise look stuck.

Result

0 keys held. Most at once: 0.

What this means

Most at once
-
Ordinary keys
-
Chosen combination
-

Next step Next: check those keys for double pressesPlay on a pad too? Check its buttons and sticks

All 20 checks

Key combinations to hold 10

  • W, A, S, D, Left Shift and Space Move, sprint and jump at once, the left-hand chord of a first-person game. Shift travels in the modifier byte of a USB report, so this uses five of the six key-code slots. A key that stays dark here points to the key matrix and not to the USB limit.
  • W and D held, then Q, E, R, F, C and Space in turn Running diagonally while you reach for an action key. Which third key jams differs between brands and models, so keep W and D down and tap each neighbour once. The page lists every tap that failed to arrive, which tells you where not to bind reload.
  • Q, W and A: three corners of a square A phantom key needs three closed switches at three corners of a rectangle in the wiring, and the phantom appears at the fourth corner. Hold these three and watch the key list. The wiring rarely follows the keycaps, so repeat with other blocks: E, R and D, or U, I and J.
Show all 20 checks (17 more)

Key combinations to hold, continued

  • Up, Left and Space Jump while moving diagonally on the arrow keys. Only three keys, and three is all it takes to jam a board with no diodes. If Space never lights, try Up with Right, then move jump to another key and test that.
  • Both Shift keys, then A to Z Modifier keys are typically read apart from the letter matrix, which is why Shift seldom blocks anything. This check puts that to the test: hold both Shift keys, type the alphabet once, and the page lists any letter that did not arrive.
  • W, A, S, D and all four arrow keys Two players sharing one keyboard. Eight ordinary keys is two more than a basic USB report carries, so a board limited to six codes stops at 6 here however good its switches are. Some gaming boards give only these eight keys their own diodes.
  • A, S, D, F, J, K and L: the seventh key Seven home-row keys and no modifiers. Add them one at a time. The USB boot report has room for six key codes, and the HID specification tells a keyboard to send a rollover error in place of a seventh. A count that stops at 6 is that limit showing.
  • S, D, F, J, K and L as one chord Six keys struck together, three fingers of each hand, like a braille typewriter's six dot keys. Braille entry on a computer keyboard can need all six at once. Six ordinary keys also fills a basic USB report exactly, so only the matrix can block this chord.
  • Eight home-row keys and Space Nine keys under ten resting fingers: A, S, D, F, J, K, L, the key to the right of L, and Space. Stenotype writes whole syllables as chords and needs full n-key rollover. A count of 9 here shows the board reports well past six keys.
  • Both palms flat on the letter rows No pattern, only a ceiling. Press both palms across the three letter rows and read the maximum. The page reports the most keys it saw, such as 23. It cannot prove there is no limit, because a full n-key rollover board never runs out.

What your maximum means 4

  • A maximum of 2 or 3 keys Two-key rollover is the floor: any two keys register, and a third may be refused. One combination that stops at 2 is ordinary jamming. If every combination you try stops at 2 or 3, the board is built to that minimum.
  • A maximum of 4 or 5 keys Some boards are wired so that keys that often follow each other in typing share a line, which one reference describes as giving four or five keys for common sequences. Odd combinations can give fewer. The result changes with the combination, so test the keys you play on.
  • A maximum of exactly 6 keys Six is the number of key codes in the USB boot keyboard report: 8 bytes, one for the eight modifiers, one reserved, six for keys. Add both Shift keys. If the count rises to 8 yet never passes six ordinary keys, you are reading the report limit, often written 6KRO.
  • A maximum of 7 keys or more More ordinary keys than the basic report holds, so the keyboard is sending a larger report of its own, which is what a maker means by NKRO over USB. Ten fingers is the ceiling for deliberate chords; flat palms can go past it. The page shows the most it saw, not proof of no limit.

Rollover readings that need a second look 6

  • A third key that never lights What players call ghosting: a key that fails to register while others are held. Engineers call it jamming or blocking. The keyboard refuses the third key because accepting it could produce a phantom fourth. It belongs to that combination on that model, not to wear, so rebind the action to a neighbour that registers.
  • A key lit that you never pressed A phantom key, the older and stricter meaning of ghosting: three held keys close a loop in the matrix and a fourth appears at the last corner. Modern boards block the third key instead, so this is rare. Note the three keys you held and the extra one, then repeat it.
  • A key that stays lit after you let go Usually the page and not the keyboard. A web page learns of a release only if it is still in front when the key comes up, so a system shortcut or a window switch mid-hold leaves the key marked. Press it again or use Clear.
  • Fn held and nothing counted Fn is typically handled inside the keyboard and sends no code of its own, so no web page can count it. It changes what other keys send instead. Leave it out of rollover checks and test the key it sits beside.
  • A key named differently from its keycap The page names keys by physical position, not by the character your layout types, so on an AZERTY board the key it calls W is printed Z. Position is what matters for rollover, because jamming happens in the wiring under the keys.
  • A different maximum on another connection How many keys arrive depends on the report the keyboard sends as well as on its switches. USB boot keyboards are limited to six keys, while the older PS/2 connector has no such limit. If your board offers a second connection or a rollover mode, test each one.

How this list was compiled: Table written for this page. The definitions of key rollover, n-key rollover, two-key and multi-key rollover (the article's figure of four to five keys for common sequences stands in a paragraph it marks as needing a citation, so the table gives it as one reference's description and not as a rule), ghosting (a phantom fourth key when three corners of a rectangle of switches in the matrix are closed), jamming (a modern keyboard ignores the third key instead, and which keys jam differs between brands and models), a diode on every switch as the cure, gaming keyboards that give diodes only to W, A, S, D and the arrow keys, Ctrl, Alt and Shift typically being read apart from the character matrix, stenotype needing full n-key rollover, braille entry needing as many as six keys at once, and the two-player game that shipped with its own key-jamming test, are from https://en.wikipedia.org/wiki/Key_rollover (the article that Rollover (keyboard) redirects to; last edited 15 July 2026, read 2026-09-19). That USB boot keyboards are limited to six-key rollover and that the PS/2 connector supports n-key rollover is from https://en.wikipedia.org/wiki/USB_human_interface_device_class (last edited 8 July 2026, read 2026-09-19). The layout of the boot keyboard report (8 bytes: byte 0 the eight modifier keys, byte 1 reserved, bytes 2 to 7 six key codes) and the rule that a keyboard sends a rollover error in every key field when more keys are down than the report holds, with modifiers still reported, are from Appendix B.1 and Appendix C of the Device Class Definition for HID 1.11 at https://www.usb.org/sites/default/files/hid1_11.pdf (read 2026-09-19). That a key's code names its physical position whatever the layout (the key coded KeyW is labelled Z on an AZERTY keyboard) and that Fn is typically a hardware key with no code of its own are from the W3C UI Events KeyboardEvent code Values Recommendation at https://www.w3.org/TR/uievents-code/ (read 2026-09-19). Browser support for that property was read on 2026-09-19 from https://github.com/mdn/browser-compat-data, file api/KeyboardEvent.json, entry api.KeyboardEvent.code: Chrome 48, Firefox 38, Safari 10.1. On this site ghosting is used in the players' sense, a key that fails to register, which the article calls jamming; the article's own ghost is called a phantom key here. The combinations themselves, and the advice on each, are this page's own. Licence: own work

How it works

Hold keys down and this n-key rollover test counts how many your keyboard reports at once, plus the most so far and each key's name. Ten combinations show which keys block each other. A phone needs a physical keyboard connected.

Read the full guide

What the key rollover tester counts

Key rollover is the number of keys a keyboard can register together. Click the test area, press keys one at a time and keep them down. The counter shows how many the browser sees and the most it has seen, split into keys and modifiers. Press Esc or Stop to end the run.

Test the combinations you play on

Pick a pattern under Check to run. W, A, S, D, Left Shift and Space is sprint and jump in a shooter. Up, Left and Space is only three keys, and three is enough to jam a board with no diodes. A, S, D, F, J, K and L: the seventh key shows whether the count stops at 6, the limit of a basic USB report.

  • Leave Ctrl out of any chord. Ctrl with W closes the tab in most browsers.
  • Blocked keys differ by model. Hold W and D, tap keys round them and bind actions to those that register.
  • An n-key rollover keyboard can still read 6 in a six-key mode. Test each mode or connection its manual lists.

Questions and answers

What is n-key rollover?

The keyboard scans every key independently, so each press registers however many others are down. Boards without it share wiring and are only sure of two at once. USB's basic report carries eight modifiers and six ordinary keys, so passing more takes a larger report.

Is this a keyboard ghosting test as well?

Yes. A key ghosting test looks for a key that fails to register while others are held. Engineers call that jamming: the board refuses a third key because accepting it could produce a phantom fourth. Hold a combination: any key still dark is blocked.

Can a keyboard NKRO test in a web page prove full rollover?

No. It reports the most keys it saw, and nobody can press every key at once. It also sees only what the browser passes on: Fn sends no code. A maximum above six ordinary keys shows the board sends more than the basic report.

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