Is that 320 actually 320?

A label in the file name doesn't prove it. Tune Check reads the actual frequency content. A real 320 carries detail up near 20kHz. A relabelled fake stops well below that, whatever the tag says.

Look for a frequency cutoff. Low-bitrate encoding throws away high frequencies to save space, and converting that file to 320 afterward doesn't bring them back. Tune Check finds that cutoff and flags it.

No. Everything runs locally, in your browser. The only outside call is a text lookup of the track's name, and only for a file that comes back below 320. On an untagged file that name is the file name without its extension. No audio ever leaves your machine.

The free tool here checks 20 files in a run. A Bangerz Army membership skips the scan entirely and gives you the verified 320s from the catalogue.

Yes, and WAV, M4A, AAC, OGG and Opus. Lossless formats can still hide a lossy source: a file that started as a low-bitrate MP3 and got wrapped in FLAC or WAV without ever getting the deleted detail back. AIFF and ALAC are the two exceptions right now, because Chrome has no decoder for either and everything here runs in your browser.

It cannot tell you where a file came from or who made it. A cutoff is evidence about one thing: how much of the top end survived whatever encoder touched the file last. The bitrate a file declares is a label, and a label can be rewritten. The spectrum is a measurement, and a measurement can still have an innocent explanation, such as a dark master or a vinyl rip. A lossless file is not bad because it does not look like a 320 kbps MP3. Tune Check prints the number and the picture, and stops there.

It is the height of the file, in kilohertz, and it appears on files Tune Check marks red. A real 320 runs to about 20 kHz and carries real sound in its top octave. A file that stops lower, or that reaches 20 kHz with nothing living above 16 kHz, is not the 320 you were promised, whatever its label says. Tune Check prints the number and the picture, and you can look at both.