The tySplineRepair modifier can be used to repair common issues with splines.
Close open splines: when enabled, open splines (with 3 or more knots) will be closed.
Flatten knots: when enabled, spline knots will be projected (and flattened) along the specified axis.
Along X/Y/Z: the flatten axis will be the specified world-space axis.
Along nearest axis: the flatten axis will be the world-space X/Y/Z axis closest to the computed spline normal.
Along normal the flatten axis will be the computed spline normal.
Per-object/Per-spline: the flatten procedure will be performed on either a per-spline basis (meaning each subspline will be flattened individually), or a per-object basis (all spline knots will be flattened together).
Full projection: when enabled, all knots will be fully projected onto the plane perpedicular to the flatten axis. When disabled, the height of each knot in plane-space will be set to the average height of all knots in plane-space.
Remove coincident knots: when enabled, all coincident (perfectly overalpping) knots will be removed.
Clip splines: performs a spline clipping operation where all overlapping spline segments (along the computed normal of the spline) will be resolved with new knots/segments, relative to the specified operation and fill type.
Per-object/Per-spline: the clipping procedure will be performed on either a per-spline basis (meaning each subspline will be split individually), or a per-object basis (all segments intersections will be resolved together).
If “clip splines” is enabled, splines will be pre-flattened along their normal.
Display knots: when enabled, spline knot points will be displayed in the viewport.
Display knot indices: when enabled, spline knot indices will be displayed in the viewport.