A double-click on a single click is the most common mouse fault, and it usually comes from a worn left-button switch. But not every double-click is a hardware failure, so rule out the cheap causes first.
1. Check the Windows double-click speed
In Control Panel > Mouse > Buttons, a “Double-click speed” slider set too fast can turn two separate clicks into a double-click. Move it to the middle and test again. “ClickLock” on the same page should be off.
2. Try another port and another computer
If the problem follows the mouse to another computer, the mouse itself is at fault. On wireless models replace the battery and plug the receiver into a port close to the mouse.
3. Measure it in the browser
On the Mouse Test page, press the left, right and middle buttons one at a time. “Double-click risk” shows a dash at first; it does not say “no risk” before you have clicked. A second press within 90 ms of the first counts as a suspicious event. For a longer run, use the 15-second mouse diagnostic tab on the same page.
4. Read the result correctly
“No suspicious double-click seen” does not prove the mouse is sound. The fault can be intermittent and may not show up in a short run. If you still suspect it, repeat the test on different days and at different speeds (slow and fast). A browser only sees events passed on by the operating system; it cannot measure the physical number of presses.
5. Replace the switch or the mouse
Once confirmed, there are two routes: if you can solder, replace the left-button switch (usually an Omron); otherwise use the warranty. On a low-priced mouse, buying a new one is usually the more sensible choice.
If you also want to measure click speed
The CPS Test shows how many times you click in 5 seconds and your clicks per second (CPS). CPS alone says nothing about a double-click fault; it only measures speed.