Limitations

Some limits of HARP follow from processing remotely, and others are features we have yet to build. Requests and contributions are welcome as issues.

Processing

HARP processes files, not streams. A model receives whole files and returns whole files, so HARP cannot process live input, follow the transport of a DAW, or respond to automation. It is an external editor rather than a plugin, and offers no VST3, AU, or AAX version.
Results replace the original. Sending a result back to a DAW overwrites the file behind the region, with no undo in HARP (see Protecting the Original).
An app runs one job at a time. Requests from several users to the same app wait their turn.
Jobs have time limits. PyHARP stops a job after 15 minutes by default, and a ZeroGPU request must fit within the remaining daily allowance of the caller.
Progress is not reported. HARP shows the state of a request, but not the progress bars, notices, or warnings an app reports through Gradio, which reach only the page of the app.

HARP needs a network connection, except to reach an app running on your own machine.
Your audio leaves your machine. Every input is uploaded to whoever hosts the model. For material that must stay private, host the model yourself (see Hosting Elsewhere).
Hosted models can change. A Space can sleep, run out of allowance, fail, or be taken down by its owner. A sleeping Space takes a minute or two to wake.
Custom paths cannot sign in. HARP cannot log in to a Gradio app protected by a password.

Audio tracks accept WAV, AIFF, FLAC, OGG, and MP3 files, and MIDI tracks accept .mid and .midi files. Other files travel through a generic file input or output, which HARP shows but does not play.
Controls are limited to sliders, number boxes, dropdowns, multiselect dropdowns, toggles, text boxes, and file pickers. Other Gradio components, such as images or radio buttons, have no counterpart in HARP.
Text is an input only. A model that produces text returns it as a file.
Labels are drawn over an output track of the same request, so a model that returns labels also returns the media they describe.

Only some DAWs open regions in HARP. REAPER, Logic Pro, Ableton Live, and FL Studio use it as an external editor. Pro Tools, Cubase, Audacity, and Adobe Audition exchange files with HARP instead (see Setting Up HARP).
Most DAWs open only audio in an external editor, so MIDI is exchanged as files (see MIDI).
The Windows executable is not code signed, so Windows warns before running it the first time.
Linux builds need glibc 2.35 or newer, and run under X11 or XWayland.

HARP calls the Gradio API, which apps built on Gradio 4.x or earlier do not offer. Apps on Gradio 5.x work, but cannot tell HARP why a job failed.
HARP and PyHARP are released in pairs (see Versions), so an app is best deployed with the PyHARP that its users expect.