Custom GUI Visualizer
Drag your GUI art onto the container window until its slots line up, and leave with both halves of the setup: the glyph height, ascent and title shift Java draws it with, and a ready-to-paste gui.yml entry for Bedrock.
Drag the texture to position it, Alt-drag (or right-drag) to resize it. Arrow keys nudge 1px (Alt = 0.5px, Shift = 8px), +/- nudges the glyph height 1px (Shift = 8px).
Upload the texture your GUI glyph uses, at its native resolution, and pick the row count of the menu it belongs to.
Drag the art into place and Alt-drag to resize it, until its slots sit on the grid. Everything else follows from that.
Java side: copy the glyph values - height, ascent and title shift - into the Nexo glyph and its container title.
Bedrock side: copy the entries into plugins/Scaffolding/gui.yml, run /scf reload and reconnect.
gui.yml entry
Add a texture to generate gui.yml entries.
Java draws a glyph at its font height, not at the texture's file resolution, so set Glyph height to your glyph's value or the preview will be the wrong size. The exported size and offset pin the art, so Scaffolding skips its own auto-fit and the game matches this preview exactly.
Background decides how much of Bedrock's own window backdrop stays behind the art. Bedrock draws one backdrop behind the storage half and the player-inventory rows together, so it can only be dropped wholesale; Scaffolding splits it. By default the window keeps its backdrop. Pick Inventory rows only when your art replaces the storage half but you still want the inventory rows framed the way Java frames them, or None for bare slot cells. The same values work as a top-level background in gui.yml to change the default for every entry.
Offsets use large-window coordinates, center-anchored; Scaffolding handles the small-panel shift. Set Rows to the row count of the menu this art belongs to before you position it: the overlay centers on the window, and the window is 18px shorter per row below 9x3 / 9x6, so the same offset sits 9px higher per missing row. Rows 1-3 use the small window, 4-6 the large.