Sending to your printer
Once a slice succeeds, the result button bottom-right offers three things:
- Download G-code — save the file and move it yourself (SD card, USB, your own upload).
- Just upload — copy the file to the printer without starting it.
- Upload & print — copy it and start the print, after you confirm.
It remembers which you chose last, so the one you use most becomes the default click. Upload & print still asks every time, because it moves real hardware. And once you change anything after slicing, the button steps aside until you re-slice, so a file that no longer matches the plate is never sent.
Downloading works everywhere and needs no setup. Uploading needs a connected printer.
What's supported today
Klipper via Moonraker — Mainsail, Fluidd, and anything else that speaks Moonraker. This is the connection that detects, probes, uploads and starts prints.
OctoPrint, PrusaLink and Bambu Lab can be saved on a printer profile, but sending to them isn't implemented yet. Their status shows as unsupported rather than pretending to work. Download the G-code and upload it through their own web interface in the meantime.
Connecting a printer
Settings → Printers → Add printer, then either press Detect with the printer's address, or fill in the connection section by hand:
- Host — a hostname (
mainsailos.local) or an IP (192.168.1.42). It can include a scheme or port if yours is unusual. - Port — normally left alone.
- API key — only if your Moonraker requires one.
Detect is the shortcut worth taking: it confirms the machine is reachable and fills in bed volume, nozzle and kinematics from the printer.
The status dot
Every printer card and the home screen show a live status dot, re-checked periodically.
| Dot | Meaning | What to do |
|---|---|---|
| Green | Online | Nothing |
| Amber | Checking, the host answered with an error, or the connection type is Not supported yet | Wait, check the API key — or download and upload manually |
| Grey | Offline (nothing answered), or a local profile with no connection | Check the address and that the printer is on — or nothing, if it's simply switched off |
Offline is grey rather than red on purpose: a printer that's switched off isn't a fault. Hover a card for the reason behind its status, and click it to open that printer's settings.
The dot reflects an actual probe, not a saved flag. If it's green, something answered just now.
Why the desktop app connects better
In the desktop app (and on a self-hosted server) the probe and the upload happen in the native process, over the OS's network stack.
In a plain browser tab they can't. Moonraker doesn't send the CORS headers a browser demands, so a direct request from a web page is usually blocked — even though the printer is sitting right there and reachable. When that happens you'll see a distinct blocked by browser security status rather than a misleading "offline".
If you print from the same machine you slice on, use the desktop app. If you want the browser, self-host — then the server does the talking and the browser never has to.
While it uploads
A pill at the top of the scene fills as the upload runs, then turns green or red in place. Failure carries the reason from the printer — a bad API key and an unreachable host read differently, on purpose. If you chose to start the print rather than just send it, the app marks the moment with a brief celebration.
Filenames
Downloads are named after the plate. On the desktop you get a normal Save-As dialog; on iPad, the share sheet; in a browser, a normal download.