How-to · When something breaks

Fix a design that will not open

Recover when a design will not open, or a part in an open design will not load.

A design will not open, list, activate or close, or a part inside it will not load, and you want a way past it.

A design that will not open, list, activate or close

Look at the tab strip's right edge. A failure there shows as a short line of red text, truncated to fit.
Point at that text to read the whole message in a tooltip.
There is no retry control here. Tell the session what the message says. Only the session can fix what it names.

The message says which of these you have:

The design has not been built. Ask the session to build it, then open it again from the + menu.
The newest build failed and no earlier build exists. The session reads the build log, fixes the design and builds again.
The build is incomplete or its manifest is unreadable. Ask the session to build the design again.
The folder has no design.toml. The design was renamed or removed.

A never built line in the tab strip's + menu is not a failure by itself. It becomes a failure once you try to open that entry.

Look for a small notice over the viewer, naming the part.
Press Try again. The design keeps rendering meanwhile, but you cannot pick a face or draw on that part until the retry succeeds.

See Modes for what CAD mode is.