Short answer: a dead key produces nothing when you press it, and a sticky key does the opposite — it stays down after you let go, keeps repeating, or fires when you never touched it. Both are usually a contact problem under that one key. To find which key is failing, open the keyboard check, press each suspect key once, and read what shows on screen: a dead key lights up no keydown at all, while a stuck key lights up a keydown that never gets its keyup (it stays highlighted) or fires without a press. Rule out the Sticky Keys accessibility feature and software first, because those imitate a stuck key without a single thing being wrong with the hardware. Keep in mind the check reads the key events your browser receives — it can show a key that never registers or one that will not release, but it cannot measure contact resistance, the debounce window, the matrix scan, or polling rate.
Dead vs sticky: two different failures
Name the symptom before chasing a fix, because “dead” and “sticky” point at opposite ends of the same contact:
- Dead (no registration). One clean, deliberate press produces no character and no on-screen response. The contact is not closing, so the firmware never sees a press to report.
- Sticky / stuck (will not release, or self-fires). A press registers but the release does not, so the key acts held — it repeats, holds a modifier down, or drops characters when you did not press it. The contact is closing but not cleanly breaking, or is bridged by dirt.
- Not the same as chatter. A key that types twice from one tap is a third pattern — switch bounce, not a dead or stuck contact. If that is your symptom, the key chatter guide is the one to read.
Rule out settings and software first
A surprising amount of “dead” or “stuck” behavior is not the switch at all. Clear these before you open the keyboard:
- Sticky Keys and Filter Keys. Windows Sticky Keys deliberately holds a modifier (Shift, Ctrl, Alt) down after a single press, and Filter Keys can ignore brief or repeated presses — both mimic a stuck or dead key exactly. Turn them to a known state (the macOS equivalents live under Accessibility → Keyboard) and retest.
- A stuck modifier or remap. If everything you type comes out wrong or shortcut-like, a modifier may be logically held or remapped. Tap each of Shift, Ctrl, Alt, and the Windows/Command key once and watch them clear in the keyboard check; check any remapping tool you run.
- Layout, not fault. A key that “types the wrong character” is often a keyboard-layout mismatch (US vs UK vs another locale), not a dead key. Confirm the layout matches the physical board.
- Test across apps and paths. Type the key in a bare text field and the address bar, not one program. Then change the path — another USB port, a different cable, or fresh batteries and a closer receiver for wireless — to separate the keyboard from the computer.
How to test which key is failing
Once settings are clear, the keyboard check turns a vague “something is off” into a specific key. Open the keyboard check and work one key at a time:
- For a dead key, press it once, slowly and deliberately. If the matching key stays dark — no
keydown, no highlight — while its neighbors light normally, that key is not registering. Repeat a few times to be sure it is the key and not a missed press. - For a sticky key, press and release it once. If it lights on the press but does not clear on release — a
keydownwith nokeyup, or a key that keeps registering after your finger is gone — the release is not breaking the contact. - Isolate keyboard vs computer. If the same key fails on another port, cable, or machine, it is the keyboard. If it works elsewhere, suspect the driver, the port, or software on the original computer.
What the browser can and cannot see
A web page sees only the key events your system sends it — keydown and keyup, by physical key — after the operating system and driver have handled them. So the keyboard check can show you a key that never registers, or one whose press never releases: real, repeatable symptoms you can act on and record. What it cannot do is measure the physical contact resistance, the debounce window the firmware applies, the matrix scan, or the polling rate — none of those are exposed to a browser. Anything claiming to read a switch’s health or timing in milliseconds from a web page is inferring from the events, not measuring the hardware. For everyday rate-style checks rather than per-key events, the keyboard counter and typing test are where a dead or sticky key usually first shows up as a dropped or doubled letter.
If it is the switch
Once settings and software are ruled out and a key repeatedly reads dead or stuck, treat it as hardware. Cleaning fixes many early cases, and sticky keys especially: power down, pop the keycap, and blow out dust and debris with compressed air — a spill or crumb under one key is a classic cause of both a key that will not press and one that will not release. A key that stays dead or sticky after cleaning is failing: on a hot-swap mechanical board you can replace that one switch, while on a soldered or membrane keyboard it usually means a board-level repair or a new keyboard. If the keyboard is in warranty, capture the repeatable symptom — a short screen recording of the keyboard check showing the key fail to register or fail to release — the same way you would build evidence for any warranty or RMA claim. Not sure how a run is judged first? The method page explains what a completed observation does and does not certify.