Troubleshooting
The model
"Outside the build area" — part of the model is beyond the print volume. Use Centre on bed, or scale it down, or check your printer profile's bed size is right. The check uses your bed's actual shape, so a round bed isn't treated as a square.
"Overlaps another object" — two parts intersect. Press A to re-arrange, or move one by hand. Parts that merely touch edge-to-edge don't trigger this.
The model floats above or sinks into the bed — turn Gravity (G) on, or use Drop to floor in the move tool.
A 3MF came in as several objects — that's correct. A 3MF is a scene, and each build item becomes its own object so you can place them independently.
The file won't open — Cold Crabby reads .stl, .obj and .3mf up to 500 MB. Anything else (STEP, F3D, blend) needs exporting to one of those first.
Slicing
The slice failed — the status line carries the reason. Most often it's a model with holes or flipped normals. Repair it in your CAD tool, or run it through a mesh repair service, and try again.
It's taking a very long time — big models with fine layers and dense infill are genuinely slow. In a browser tab it's slower still, because the whole engine is running inside the page. The desktop app is markedly quicker on heavy models.
Nothing seems to change when I re-slice — identical input produces identical output, and Cold Crabby will reuse a cached result rather than repeat the work. Camera movement and the thumbnail don't count as changes. If you changed a setting, the result will differ.
The preview
Sparse or missing top surfaces — increase top layers (Process → Surfaces), or infill density so the top has something to build on.
Supports where I don't want them — raise the overhang threshold angle, or switch support type. Check the preview again afterwards.
Stringing between parts — enable travel moves in the preview to see the paths, then look at Retraction on the printer profile.
Printers
The status dot is red — nothing answered. Check the address, that the printer is powered on, and that you're on the same network.
The status dot says blocked by browser security — you're in a browser tab and the printer doesn't send CORS headers. This is a browser restriction, not a fault. Use the desktop app, self-host, or download the G-code and upload it through your printer's own web interface.
"Unsupported" — that connection type isn't implemented yet. Only Klipper via Moonraker can upload today.
The upload was rejected — usually a wrong or missing API key. The notification carries the printer's own message.
Settings and profiles
My profiles disappeared — if you were running in a browser tab, they were stored in that browser. Clearing site data removes them. Export a backup from Settings → General → Backup & Export, and consider the desktop app or a self-hosted server, where they live outside the browser.
A setting I read about isn't there — options hide when they don't apply. Thin walls, for instance, only appears with the classic wall generator, since the Arachne generator handles thin features by construction. Search with ⌘/Ctrl + F; if it still doesn't appear, something it depends on is switched off.
I want to start clean — Settings → Danger Zone can clear slice history, reset profiles to defaults, or reset the whole app. Each asks for confirmation.
Performance
The 3D view is choppy — in Settings → General, lower Render resolution and Preview detail, and turn Anti-aliasing off.
A big G-code preview is slow to scrub — switch from all layers to current layer only.
Still stuck
Check what version you're on in Settings → General, then open an issue on GitHub with the model, your settings, and what you expected.