Convert your MP3s to WAV to use them in audio or video editors, or on equipment that only accepts this format.
No sign-up and nothing uploaded to a server: everything happens in your browser. See for yourself.
No. The resulting WAV keeps exactly what was in the MP3, but with no additional compression.
Because WAV doesn't compress the audio. One minute of stereo usually weighs about 10 MB.
No. Everything is processed in your browser.
Some editing programs, mixing consoles and professional audio equipment only accept WAV. Converting your MP3 to WAV lets you use it with them.
Keep in mind that going from MP3 to WAV doesn't recover the quality the MP3 already lost: the file will be bigger, but the sound will be the same.