Does it preserve existing defs?

It inserts a new defs block at the start of the SVG.

What if there is no shape?

The pattern is still inserted, but no shape receives the fill.

Yes. Copy the SVG and change the pattern width and height attributes.

Edit

Insert an editable SVG pattern definition and apply it to artwork.

Insert an editable SVG pattern definition and apply it to artwork.

Choose an SVG file, paste SVG markup, or load the sample to begin.

Page context

SVG Pattern Editor inserts an editable SVG pattern definition and applies it to artwork.

The tool adds a defs pattern named svgkit-editable-pattern and applies it as a fill to the first renderable shape it finds.

It is not a full pattern design UI. The generated pattern can be edited manually or expanded with controls later.