Why even waste time on this, aren't there many similar tools?
No. All the tools I have found are either full of ads, require uploading, or even worse: Ugly, unresponsive and unintuitive.
I have made this tool primarily for my needs, but it spiraled out of control and became whatever you are seeing right now.
I was unable to find a satisfactory spectrogram app / website / program, since all of them are either far too complex for my liking and needs, don't work as they should, or require a multiple gigabyte installation. No more.
This tool has a bunch of functions that I needed, or anticipate that I will need in the future, and equal number of ones that I don't or never will.