How to paste a .schem with WorldEdit

Every SchemSmith build downloads as a .schem file (Sponge schematic, version 3) with Minecraft Java 1.21.11 blocks. This guide takes it from your downloads folder into a Paper or Spigot server, or a single-player world, with WorldEdit.

Short version

Put the file in plugins/WorldEdit/schematics/ on the server.
In game: //schem load <name>
Stand where the build's corner should go: //paste -a
Wrong spot? //undo

Before you start

Minecraft Java 1.21.11. SchemSmith's blocks and exports are made for this version (the file's DataVersion is 4671). On an older server, blocks that version doesn't have can't be placed.
WorldEdit 7.3 or newer, or FastAsyncWorldEdit (see big builds). Older WorldEdit versions can't read schematic version 3; the app's Export menu also offers a .schem v2 for them.
Permission to use it: operator status, or the WorldEdit permissions worldedit.schematic.load, worldedit.schematic.list, worldedit.clipboard.paste, worldedit.clipboard.rotate and worldedit.history.undo.

1. Download the file

From a build page on Builds: Download .schem. The file is named after the build, for example neuschwanstein-castle.schem.
From the app: Export ▾ in the toolbar of the 3D view, then .schem. The file is saved as build.schem, so rename it to something you will recognise, ideally without spaces (my-tower.schem). WorldEdit loads it by that name.

2. Put it in the schematics folder

Paper or Spigot server: plugins/WorldEdit/schematics/. Upload it with your host's file manager or SFTP. WorldEdit creates the folder the first time it runs; if it isn't there, create it. With FastAsyncWorldEdit the folder is plugins/FastAsyncWorldEdit/schematics/.
Single-player with WorldEdit for Fabric or NeoForge: config/worldedit/schematics/ inside your Minecraft game folder (.minecraft, or the folder of your launcher profile).

No restart or reload is needed. WorldEdit reads the folder when you run the command.

The downloaded file in plugins/WorldEdit/schematics/

3. Load it

//schem list
//schem load neuschwanstein-castle

//schem list shows the files WorldEdit can see. //schem load takes the file name; the .schem ending is optional. Loading copies the build to your WorldEdit clipboard. Nothing in the world changes yet. (//schematic is the long form of //schem.)

//schem list and //schem load in chat

4. Stand in place and paste

//paste places the build relative to where you stand. SchemSmith files carry no offset, so the build's bottom corner with the lowest X and Z (its north-west corner) lands on the block your feet are in, and the build extends east (+X), south (+Z) and up from there. Press F3 to see your coordinates. The build page lists its size as width × height × depth, which is X × Y × Z, so you can check that the space is free.

//paste -a

-a skips air. Without it, every empty cell of the build's bounding box is pasted as air, which cuts a box-shaped hole into the terrain, trees and anything else in the way. Neuschwanstein Castle has 174,944 blocks, but its box is 142 × 95 × 65 = 876,850 cells: without -a all of them are set.

The build after //paste -a, pasted from the corner you stood on

Without -a: the air in the build's box replaces the hillside

5. Turn it first (optional)

//rotate 90
//paste -a

//rotate turns the clipboard around the vertical axis by 90, 180 or 270 degrees before you paste. It turns around the corner that lands at your feet, so a rotated build extends in a different direction from where you stand. Rotations add up: two //rotate 90 make 180. //flip mirrors the build instead.

6. Undo

//undo

Removes your last paste and puts back what was there. //undo 2 goes back two steps, //redo brings a paste back.

Big builds: FastAsyncWorldEdit

Plain WorldEdit places a paste on the server's main thread in one go. A few thousand blocks are instant, but a build like Neuschwanstein Castle (174,944 blocks) or Tower Bridge (167,334) can freeze the server for a noticeable moment while it pastes, and the Taj Mahal (1,135,847 blocks) is a lot to ask of plain WorldEdit.

FastAsyncWorldEdit (FAWE) is a drop-in replacement for WorldEdit on Paper and Spigot: the same commands, but it places the blocks in the background, so large pastes don't stall the server. Install it instead of WorldEdit (remove the WorldEdit jar) and put schematics in plugins/FastAsyncWorldEdit/schematics/.

Block limits. WorldEdit can cap how many blocks one command may change: max-blocks-changed in the limits section of plugins/WorldEdit/config.yml, with a default and a maximum. Out of the box both are -1 (no limit), but many servers set one. If a paste is cut off with a message about the maximum number of changed blocks, raise your own limit with //limit <number> (up to the configured maximum), or ask an admin to raise it. -a helps here too, since skipped air doesn't count. FAWE has its own limits per permission group in its config.yml; if FAWE refuses a big paste, look there.

Neuschwanstein Castle (174,944 blocks) pasted with FastAsyncWorldEdit

If something goes wrong

The file isn't in //schem list: Check the folder: plugins/WorldEdit/schematics/ for WorldEdit, plugins/FastAsyncWorldEdit/schematics/ for FAWE, and that the name ends in .schem. FAWE can be set up to give every player their own schematic folder; then the file goes into the subfolder named after your player's UUID.
WorldEdit can't read the file: Your WorldEdit is older than 7.3. Update it, or export .schem v2 from the app's Export menu.
Blocks are missing or wrong: The server runs an older Minecraft version than 1.21.11 and doesn't know some of the blocks.
The server freezes or the paste stops partway: Use FastAsyncWorldEdit and check the block limits.

No WorldEdit, or building by hand in survival? The .litematic download works with the Litematica mod: see how to build a .litematic with Litematica.