Focus the tester first
Only keys delivered to the marked surface can be measured; browser or operating-system shortcuts may intercept combinations.
Hold combinations deliberately
Start with two or three ordinary keys, then add keys while watching the held set and keyup events.
Test several regions
Keyboard matrices can fail on specific combinations rather than at one universal key count.
Separate software from hardware
Accessibility tools, remote desktops, browser settings, and connection adapters can change delivered events. Confirm failures in another application or device.
Build a repeatable combination matrix
Test ordinary letter clusters first, then common game or work combinations that matter to you, such as a modifier plus two nearby keys. Hold the first key, add the others one at a time, and release them in reverse order while watching the held list. Repeat the same sequence several times and in different keyboard regions. The maximum-held figure records only the largest combination delivered during this tab; it cannot prove every combination of that size works or that the keyboard supports full N-key rollover.
Interpret missing keys cautiously
A combination can disappear because of the keyboard matrix, a wireless connection, a hub, firmware, operating-system interception, remote-desktop software, or the browser. Function layers on compact boards may never expose distinct physical codes, and system-reserved shortcuts may switch applications before the page records them. First repeat with shortcut prevention off, then try a different browser port or wired mode and a separate diagnostic application. Avoid entering passwords or private text: the local event log shows logical key values even though it is never transmitted.