Audiotool has extensive Midi support.
Make sure to have your external Midi gear connected and recognized by your computer. Every device which can play Midi notes will have a Midi icon in its menu bar.
When clicking this icon Audiotool will wait for you to play a note on your Midi Meyboard. Once you have done so you can play the device with your Midi Keyboard. If you have multiple Midi Keyboards you can easily assign different Keyboard to different synthesisers. You can also connect one Midi Keyboard to multiple synthesisers. Or try to use the Notesplitter to play multiple synthesisers with one Midi Keyboard.
If you want to use an external Midi Controller to control specific synthesiser parameters, you can do so by right clicking on the desired knob inside the synthesiser and choose Learn Midi Controller from the context menu.
Again Audiotool will wait for you to turn a knob or move a slider on your Midi Controller to map it to the selected parameter.
To get the best latency possible within a web browser make sure to install the Booster.
Watch the video: Using Midi Keyboard