How to use this checklist
Ask the seller to have the laptop charged, switched on and signed in, and bring a USB stick, your phone and a pair of headphones. Open this page on the laptop itself, so the screen, speakers and keyboard you test are the ones you're buying. Work from top to bottom: the order puts the quick, visible checks first, so you can stop early if the screen or keyboard already disappoints.
Most steps take under a minute. The screen colors fill the whole display, which is the only reliable way to spot a single dead pixel; the full dead pixel test and the backlight bleed test go deeper if something looks off. Keyboard, webcam and microphone open their own tests in a new tab, so your checklist stays where you left it.
Check the battery health
A browser can't see how worn a battery is, but the laptop can tell you in a minute. Look for two numbers: how much charge the battery holds now compared with when it was new, and how many charge cycles it has done.
Windows. Open Command Prompt, type powercfg /batteryreport and press Enter. It saves a file called battery-report.html in the user folder. Open it and compare Design capacity with Full charge capacity. Below about 80 percent of the original, expect noticeably shorter battery life. Many laptops also list a cycle count in the same report.
macOS. Open System Settings > Battery and click the info button next to Battery Health to see the maximum capacity. For the cycle count, hold Option, click the Apple menu, choose System Information and go to Power.
ChromeOS. Open the Diagnostics app from the launcher. The battery section shows health and cycle count.
Red flags that should stop the sale
- A swollen battery. The touchpad sits higher than usual or no longer clicks, the case has a gap, or the laptop rocks on a flat table. A swollen lithium battery is a safety risk, not just a wear issue.
- Signs of liquid damage. Sticky keys, stains under the keycaps, or a faint sweet or musty smell. Liquid damage often looks fine at first and fails weeks later.
- A locked laptop. On a Mac, Activation Lock must be off: the seller should sign out of their Apple Account and turn off Find My. On Windows, check under Settings > Accounts > Access work or school that the laptop isn't managed by a company or school, and ask the seller to remove any BIOS password.
- Specs that don't match the advert. Compare processor, memory and storage in the system settings with what you were promised.
- A charger that isn't original and a laptop that only runs while plugged in.
Questions to ask the seller
How old is the laptop, and is there a receipt? Receipts matter for any remaining warranty and show the laptop isn't stolen. Has it ever been repaired, and by whom? Why are they selling? Ask them to do a factory reset in front of you once you've agreed to buy, so you start with a clean system and their accounts are gone.
How this check works
Everything runs in your browser, and nothing is sent anywhere unless you ask for your results by email. The screen step shows five full-screen colors that together reveal dead pixels (on white), stuck pixels (on black) and faulty subpixels (on red, green and blue). The speaker step plays a short 440 Hz tone on the left channel, the right channel or both. The battery step reads the charge level where the browser allows it, and the box at the end shows the screen resolution, processor threads and memory that the browser reports. Browsers round those last numbers on purpose, so always confirm them in the laptop's own settings.