Paste or type your text, pick a voice from the list and adjust the rate, pitch and volume sliders. Press Speak to hear it, and Stop at any time to cancel playback.
They are the voices already installed on your operating system, exposed through the Web Speech API. That is why the list differs between Windows, macOS, Android and iOS, and why installing more system voices adds more options here.
On most browsers the synthesis is fully local and nothing leaves your device. Some browsers do route certain premium or network-marked voices through an online voice service, so the tool labels those voices so you can choose a local one for sensitive text.
The Web Speech API plays speech through the system audio path and does not expose a downloadable stream, so no browser tool can save it directly. Use the Voice Recorder with a loopback input, or your operating system's own recorder, if you need a file.