Check Sketch for Feature is a useful tool to troubleshoot why a sketch is not creating a feature as you would expect.
The Check Sketch for Feature tool examines sketches for errors in contours that might prevent a feature from being created. It checks for errors that are common to all contour types, and, if you select a feature type, it also checks the contour type required for the feature type. When errors are diagnosed, the problem geometry is highlighted. It is located under Tools>Sketch Tools> Check Sketch for feature when in an active sketch.
This sketch looks as if it is ready for an extrusion to create a block, but it creates a thin feature. Using Check sketch, we select "Boss Extrusion" for the feature to check for. SOLIDWORKS alerts the user that there is an open contour in the sketch, preventing the extrusion.
It also highlights the portion of the sketch with the issue so the user can correct it.
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