WiFi Channel Advisor
Your router shipped on whatever channel the factory picked, and so did every router on your street. Five questions — your model, your country, your home, how many networks you can see, and what you own — and you get the channel and channel width to set on each band, plus where to find those two settings in your router’s own admin pages.
Straight about what this is: the channel widths and the band advice are physics and hold everywhere. The channel numbers themselves are inference — no web page is permitted to scan the networks around you, so we reason from what you tell us. That gap is precisely why we are building a desktop scanner, and why the second card on this page asks for your email instead of pretending we already measured something.