Start with one key
Open the keyboard tester and press the suspect key alone. Read the character and the code. Try another ordinary letter as a control. If both are missing, make sure the test is active and the page has focus. Fn and system shortcuts can be handled outside the browser.
Compare applications
Try the same key in a plain text editor. If it works there but not in a website, inspect browser focus, extensions and the website shortcut behavior. If the character differs, compare the operating system’s keyboard layout with the printed keycap; the physical-position code can still be correct.
Change one condition at a time
For an external keyboard, compare another USB port or its wired mode if available. Then compare another computer. Avoid changing several settings at once: a repeatable difference is more useful than a long list of speculative fixes.
Document the result
Save the test observations and note the connection type separately. A report proves what the browser saw during that session. It is not a hardware certification. If a key repeatedly fails across applications and computers, consult the keyboard manufacturer’s support and warranty procedure.
Keep both reports in Device Lab →