Soundlevel makes sound tools that run in your browser: a decibel meter, a microphone test, an instrument tuner, and a metronome. They open instantly and need no app or account. Your audio is never uploaded, and the metronome doesn't use the microphone at all.
We follow the same measurement standards as hardware sound meters and explain their limits on the accuracy page.
The site is free and is supported by ads and affiliate links.