What this checks
Laser fading test. One flat tint. Edges lighter than the center are uneven output, not a measurement of remaining toner.
Read laser sheets by repetition. A mark that comes back at an even interval often follows a roller or a drum. The interval is a clue for a technician, not a part number from this site.
A browser can draw a page and hand it to the print dialog. It cannot talk to the printhead, read a toner chip, or start a cleaning cycle. Those commands belong to the printer and its driver. If a button on this site cleaned your nozzles, it would be pretending.
How to use it
When a length matters, print at 100 percent or Actual size. Turn off Fit to page, Shrink to fit, and Scale to fit. Then put a ruler on the 100 mm bar. If that bar is not 100 mm, every other judgment about size is early. The preview on the screen is scaled to fit the window. Only the paper counts.
The screen is red, green, and blue light. The printer is ink or toner on a sheet. They will not match, and this site does not build an ICC profile. Use the patches to see whether a color is missing or wildly shifted, not to approve a brand color.
A gap in a single color row points at that color: the nozzles, the cartridge, or a setting that turned the color off. A gap that cuts every color in the same place can be a scratch, a dirty roller, or damage in the scan you photographed. A whole page that is pale is a different problem again: draft mode, a low supply, or the wrong paper type. One sheet does not name the part.
What it cannot prove
On a laser printer, a mark that repeats down the page often matches the circumference of a drum, a roller, or a fuser. This page will not tell you which. Write down the distance between repeats and stop there. On an inkjet, a thin white line through one color is more often a nozzle. Do not swap those stories.
If nothing prints, the pattern is irrelevant. Check the queue, the selected printer, and whether the device is paused or offline. Then print the operating system’s own test page. A page from Windows, macOS, or the printer panel that also fails is not a problem with this website.
Borderless printing is a printer feature, not a browser feature. Edge bars that stop short of the knife are the unprintable margin or a scale setting. Forcing borderless in the driver can also scale the page. Measure the bar after you change that setting.
Questions
Can this page tell me the drum is dead? No. It can show a repeating mark. The distance between marks is what a manual uses.
The black block is brown. Is that normal? Toner and paper can shift black. Compare it with the gray steps before you replace a cartridge.
Does ghosting mean the fuser? Often people look there. This site will not say so from one sheet.