Some programs only take WAV: older audio editors, many samplers and DJ tools, CD-burning software, phone systems and a lot of game engines. This tool decodes your MP3 files and writes them as standard PCM WAV, the uncompressed format every audio app can open.
Decoding uses your browser's built-in MP3 decoder, at the MP3's own sample rate (usually 44.1 kHz), so the timing and pitch stay exactly the same. You choose 16-bit, which matches CD audio and opens everywhere, or 24-bit for editing software that prefers it. The WAV is written directly in the page; nothing is uploaded.
Honest limits: WAV can't bring back detail the MP3 encoder already removed, so the WAV sounds the same as the MP3, just in a format more apps accept. Expect files about 5 to 10 times larger: around 10 MB per minute of stereo at 16-bit, 44.1 kHz. ID3 tags (title, artist, cover art) are not carried over.