It fixes clipping at rest. In poses it measures (10 stress poses or your animation) and hides the skin the outfit covers, which removes most of what shows. Clipping in poses comes from the weights, and moving cloth at rest cannot remove it. An optional pose round adds a little room where it helps and is kept only when it does.

One Ctrl+Z undoes a Fix. The fix is a shape key named ClipFix: turn it down to compare or press Reset to remove it at any time, and Apply it when you are ready to export. The body mesh is never changed (hiding skin uses a vertex group and a Mask modifier), meshes in Hair and Accessories never move, and only the garments in the list get a ClipFix key.

Yes. VRM and VRoid rigs are recognised, separate faces and hair are left out of the garment list, and the export check covers the 4 bones per vertex VRChat and Unity expect. Cloth on its own skirt or hair bones is listed apart, because PhysBones move it at runtime.

Yes, with one step from you. ClipFix fixes the garment's own mesh, then checks it with its modifiers on. If a modifier still pulls cloth into the body, the report names it and says what clears it: for Subdivision Surface, press Reset, apply the modifier and press Fix again (Blender can only apply it to a garment without shape keys of its own); for Solidify, set it to grow outward. In our tests (five modifiers on two outfits) that cleared it in every case but one, where 2 skin points were left.

ClipFix fixes outfits on the body they are on and will still clean a garment made for another shape, but it shows how much that stretched it. Outfit Refit refits clothes to a new body shape without stretching. The two work together in one file.

Blender 4.2 to 5.2. It is tested on 4.2.23 LTS and 5.2.2 and installs as an extension (Install from Disk). Pure Python, nothing else to install.