Channel Clear is a free Wi-Fi channel planner that runs entirely in your browser. Open your phone's Wi-Fi settings, read the networks around you and their channels, and type them in above. The chart draws how far each signal spreads across the band, then marks the least-congested channel left for your own router. There is no app to install, no login, and nothing you enter leaves your device.
On 2.4GHz there are really only three channels that do not overlap: 1, 6, and 11. When the routers around you crowd onto the same channel, or onto one a few numbers away, their signals bleed together and your throughput drops, which shows up as buffering video and choppy calls. Moving your router to a quieter channel is often the single fix that helps the most, and it takes about a minute.
Most tools just list which channels are in use. Channel Clear goes further: it models each network as an energy curve the width of a real Wi-Fi channel (about 22 MHz on 2.4GHz), so two routers three channels apart still register as partial interference rather than "unrelated." That is what makes it a genuine 2.4GHz channel overlap calculator, and why the recommendation lines up with what you would measure with a spectrum analyzer.
5GHz has far more room, and its 20 MHz channels do not overlap, so congestion there is about who shares the exact same channel rather than adjacent bleed. Use the band toggle to plan each band on its own; the recommendation and chart update for whichever band you are looking at, and the networks you entered on the other band are kept.