CraftTweaker

CraftTweaker changes recipes. Not through some menu, but with a script: a file is written that states what should be added, removed, or changed — and the server starts following it. It is a tool for operators, not for ordinary players.

Typical uses: disable an overly powerful item, add a recipe for something missing from the modpack, or conversely remove a recipe (for example, so players have to take a longer path). When multiple mods run on a server at once, CraftTweaker is often the only way to reconcile their recipes with one another.

Scripts are written in the ZenScript language and reside in the scripts folder in the world or in the instance. The server loads them at startup; if there is an error in them, the recipe simply won't change. That is why the crafttweaker.log file is important — errors are printed there, including the line number.

CraftTweaker is primarily a server-side tool: recipes apply to all players, even if they do not have the mod installed. On the client, it is used mainly so that players see the correct recipes in JEI.

Important rule: back up your scripts. If you lose the scripts folder after updating the modpack, the recipes return to their default state and players will notice immediately — usually because something cannot be crafted.

1. CraftTweaker is mainly a server-side mod — it is installed on the server; on players it is used for correct recipe display.
2. Find out the server loader (Forge, NeoForge, or Fabric) and download CraftTweaker from modrinth.com/mod/crafttweaker for your game version.
3. Stop the server and back up the world and the scripts folder.
4. Upload the .jar to the mods folder on the server.
5. Start the server and try the /ct help command — it must list the commands.
6. Create a scripts folder (the /ct scripts command will show where it should be) and put a simple script in it.
7. Check the script with the /ct syntax command — it will list errors without applying the changes.
8. Load the changes with the /reload command (it reloads datapacks and then scripts).
9. Verify in game that the recipe has actually changed (in JEI or at the crafting table).
10. If the change does not take effect, open crafttweaker.log — the error will be there, including the line number.
11. Tell players what changed. Recipe changes are visible to them and, without explanation, look like a server error.
12. Back up the scripts folder with every modpack change — otherwise you will lose your recipe modifications.

CraftTweaker is a tool for operators. Regular players don't need to know about it, but they will feel the recipe changes — explain them to them.
Before editing recipes, back up the scripts folder. Updating the modpack is the most common reason people lose them.
An error in the script won't crash the server, the change just won't take effect. Always check crafttweaker.log; errors are there even with line numbers.
Before loading scripts, use /ct syntax — it lists errors without applying the changes. It saves you a server restart.
Recipes apply to all players, even if they don't have the mod installed. There's no need to force them to install it (recommending it for display in JEI is enough).
A recipe change is immediately visible to players. If you don't announce it, they'll think the server isn't working correctly.
For simpler recipe edits, datapacks also exist (the vanilla way). CraftTweaker is worth using where datapacks aren't enough — for example, when you need to edit recipes from mods.