1. Check whether your Mac or just one app misses input
Click inside the keyboard tester, press a letter and then try the same key in a plain text editor. If only one app behaves unexpectedly, investigate its focus, shortcuts or input handling before assuming a hardware problem.
2. Check Magic Keyboard connection and power
For an external keyboard, confirm that it is powered and connected. Check its battery status in macOS and reconnect it if needed. Compare a supported wired connection or a second keyboard when available.
3. Review the input source and accessibility settings
An unexpected character can be caused by the active keyboard layout. Slow Keys can delay accepted input; modifier remapping can change Command, Option or Control. Check the relevant Keyboard and Accessibility settings on your version of macOS.
4. Test missing keys, repeated input and key combinations
Make a full pass through the key map. If a key repeats unexpectedly, test deliberate taps with the chatter tool. If a combination fails, compare ordinary letter groups in the rollover tool. Keep notes of the key, connection and application.
5. Decide when to seek Mac keyboard support
If the same physical key consistently fails across apps after basic checks, consult the manufacturer’s support guidance. Follow device-specific cleaning instructions and avoid removing keycaps without suitable guidance. Browser test results alone cannot determine repair needs.