diff --git a/packs/BP/scripts/classes/Commands/lib/commandError.js b/packs/BP/scripts/classes/Commands/lib/commandError.js
new file mode 100644
index 0000000..e0f25f1
--- /dev/null
+++ b/packs/BP/scripts/classes/Commands/lib/commandError.js
@@ -0,0 +1,9 @@
+import { CustomCommandStatus } from '@minecraft/server';
+import { NotAPlayerError } from '../../Errors/NotAPlayerError';
+
+export function commandError(source, err) {
+    if (err instanceof NotAPlayerError) {
+        return { status: CustomCommandStatus.Failure, message: 'construct.commands.error.notAPlayer' };
+    }
+    throw err;
+}
diff --git a/packs/BP/scripts/classes/Commands/lib/findInstance.js b/packs/BP/scripts/classes/Commands/lib/findInstance.js
new file mode 100644
index 0000000..3019d33
--- /dev/null
+++ b/packs/BP/scripts/classes/Commands/lib/findInstance.js
@@ -0,0 +1,12 @@
+import { system } from '@minecraft/server';
+import { structureCollection } from '../../Structure/StructureCollection';
+
+export function findInstance(source, name) {
+    if (!structureCollection.has(name)) {
+        system.run(() => source.sendMessage({
+            rawtext: [{ translate: 'construct.commands.error.instanceNotFound', with: [name] }]
+        }));
+        return null;
+    }
+    return structureCollection.get(name);
+}
diff --git a/packs/BP/scripts/classes/Commands/lib/requirePlayer.js b/packs/BP/scripts/classes/Commands/lib/requirePlayer.js
new file mode 100644
index 0000000..1e88e61
--- /dev/null
+++ b/packs/BP/scripts/classes/Commands/lib/requirePlayer.js
@@ -0,0 +1,8 @@
+import { PlayerCommandOrigin } from '../PlayerCommandOrigin';
+import { NotAPlayerError } from '../../Errors/NotAPlayerError';
+
+export function requirePlayer(source) {
+    if (!(source instanceof PlayerCommandOrigin))
+        throw new NotAPlayerError();
+    return source.getSource();
+}
diff --git a/packs/BP/scripts/classes/Errors/NotAPlayerError.js b/packs/BP/scripts/classes/Errors/NotAPlayerError.js
new file mode 100644
index 0000000..252fd9a
--- /dev/null
+++ b/packs/BP/scripts/classes/Errors/NotAPlayerError.js
@@ -0,0 +1,6 @@
+export class NotAPlayerError extends Error {
+    constructor(message = 'Command requires a player source.') {
+        super(message);
+        this.name = 'NotAPlayerError';
+    }
+}
diff --git a/packs/RP/texts/en_US.lang b/packs/RP/texts/en_US.lang
index c75cf37..dde3495 100644
--- a/packs/RP/texts/en_US.lang
+++ b/packs/RP/texts/en_US.lang
@@ -105,4 +105,8 @@ construct.option.materialgrabber.description=Pulls structure items from inventor
 construct.option.materialgrabber.howto=Interact with inventories using the Material Grabber item to pull structure items from them.
 construct.option.materialgrabber.grabbed.zero=§7Grabbed 0 items.
 construct.option.materialgrabber.grabbed.one=§aGrabbed 1 item.
-construct.option.materialgrabber.grabbed.many=§aGrabbed %s items.	## Insert string: number of items transferred to the player
\ No newline at end of file
+construct.option.materialgrabber.grabbed.many=§aGrabbed %s items.	## Insert string: number of items transferred to the player
+
+## CLI shared errors
+construct.commands.error.instanceNotFound=§cInstance "%1" not found.
+construct.commands.error.notAPlayer=§cThis command can only be used by players.
diff --git a/packs/RP/texts/zh_CN.lang b/packs/RP/texts/zh_CN.lang
index 00ac1ef..d978e39 100644
--- a/packs/RP/texts/zh_CN.lang
+++ b/packs/RP/texts/zh_CN.lang
@@ -106,3 +106,7 @@ construct.option.materialgrabber.howto=使用"材料收集器"物品与箱子等
 construct.option.materialgrabber.grabbed.zero=§7已收集 0 个物品
 construct.option.materialgrabber.grabbed.one=§a已收集 1 个物品
 construct.option.materialgrabber.grabbed.many=§a已收集 %s 个物品	## 插入字符串: 收集给玩家的物品数
+
+## CLI shared errors
+construct.commands.error.instanceNotFound=§cInstance "%1" not found.
+construct.commands.error.notAPlayer=§cThis command can only be used by players.