When a diagram is broken

Invalid PlantUML produces a contained error panel. The rest of the page keeps working, the render queue keeps processing, and the page never crashes.

Worth knowing: PlantUML does not report invalid source through an error callback. It renders a picture of the error and reports success. If a tool does not check for that, it will happily show you an error image as though it were your diagram. This plugin inspects the output and turns it into a real error state.

Deliberately broken (waiting to render)

Deliberately broken

With showSourceOnError: true (the default) the original source is available in the <details> block above, so you can see what you actually wrote.

The queue recovers

A failed render must not wedge the page. This valid diagram sits directly after the broken one and renders normally:

Renders fine after the failure (waiting to render)

Renders fine after the failure

Unsupported syntax

A directive the engine does not recognise is reported the same way:

Not a recognised directive (waiting to render)

Not a recognised directive

Failure is signalled by an "Error:" label and a ⚠ glyph, not by colour alone.