Reusable blocks
A bit of circuit you built once, kept by name and dropped in again whenever you need it: a voltage divider, a debounced button, the parts for your display.
Saving one
Select the parts you want (drag a marquee, or shift-click them one at a time) and choose Save as block… from the canvas toolbar's more menu. Name it and it is on the shelf.
What a block keeps is exactly what Copy would take: every selected part with its properties, its rotation and its program, and every wire whose two ends are on selected parts. A wire with one end outside the selection has nothing to attach to in the copy, so it is left out. Breadboard holes count as pins of the breadboard, so a board with parts pushed into it needs the board selected too.
A block never carries a lock. The lock is a teacher holding a starter circuit in place; a block is your own copy, and copying a locked part is how you get one you may move.
Dropping one in
Open the part panel with + or A. Saved blocks are listed under a Blocks heading near the top, each with a drawing of the real circuit on the tile. It uses the same drawing code the part tiles and the site's own bench tiles use, so a block looks like everything else in the panel.
Click a tile and the block lands in the middle of the view. Drag it and it lands where you let go, with its top left corner at the pointer and everything snapped to the grid. Either way the parts arrive with fresh ids, their internal wires remapped to them, and the whole drop is one undo step. What was dropped is left selected, so it can be moved or rotated immediately.
Typing in the search field narrows the blocks by name as well as the parts.
Renaming and deleting
Hover a block's tile (or focus it with the keyboard) and two small buttons appear at its top right: ✎ renames it and × takes it off the shelf. On a touch screen both are simply there.
Where they live
Signed in, on your account: the shelf follows you to another machine or another browser, the same way your projects do. Signed out, a block lives on this browser only, in its own storage under one key for the whole editor rather than one per project.
Either way, a block is not in the document. It never travels in a save, an export, a share link or a room, and two people in one live room each have their own shelf.
The first time you sign in with blocks already sitting on a browser, the Blocks section offers to move them to your account: Move copies them over and keeps the ones that do not fit if your plan is full, Not now puts the offer away for that account for good. Nothing moves on its own.
The free plan keeps fifty blocks on an account; Pro and the student price keep five hundred. Signed out, a browser keeps up to sixty, newest first, and clearing this site's data clears that shelf.