Just type letters, numbers and punctuation into the top box and the Morse code will appear in the bottom box, with a "#" inserted if the character cannot be translated.
You can type American Morse code into the top box using "." for a dot and "-" or "_" for a dash. The long-dash for an "L" is Unicode U+2E3A ("⸺") and the even longer dash for a zero is Unicode U+2E3B ("⸻"). Use a single space within a letter (such as a "C" which is ".. ."). Letters are separated by three spaces and words by "/" or "|". The plain text translation will appear in the bottom box. If a letter cannot be translated a "#" will appear in the output.
The "play", "pause", "stop" and "loop" buttons control the playback. You can choose between hearing the sound, seeing a flashing light, or having your phone vibrate using the "Sound", "Light" and "Vibrate" checkboxes. The vibrate option may only appear on a phone. There are also advanced options to control the pitch and speed. The "Farnsworth speed" is useful when learning Morse code as it can be set lower than the other speed in order to stretch out the spaces between characters and words whilst keeping the Morse characters fast.
This tool works well in recent versions of Chrome, Firefox, Safari and Edge. Internet Explorer is supported at a basic level: Flash must be installed and enabled (Flash often has security issues though so is best avoided). In older Safari desktop versions you need to hold the Option key when clicking the download button and give the file a name ending in ".wav".
There is a known problem with bluetooth headphones (BLE ones in particular): to conserve energy the sound cuts out when nothing is playing and then does not reconnect immediately, causing initialy dahs to turn into dits for instance. If you experience such strangeness, please try wired headphones or the speaker until this is fixed.
Right now the flashing light only works properly for "CW Radio Tone" and the download also only creates the CW tone, not the Morse sounder.