diff --git a/src/edu/kit/informatik/cardgame/model/Inventory.java b/src/edu/kit/informatik/cardgame/model/Inventory.java
index 05bc6b2..ac41812 100644
--- a/src/edu/kit/informatik/cardgame/model/Inventory.java
+++ b/src/edu/kit/informatik/cardgame/model/Inventory.java
@@ -3,6 +3,12 @@ package edu.kit.informatik.cardgame.model;
 import java.util.*;
 import java.util.stream.Stream;
 
+/**
+ * Player inventory. Contains {@link CardCategory#RESOURCE resources} and {@link Item items}.
+ *
+ * @author Arne Keller
+ * @version 1.0
+ */
 public class Inventory {
     /**
      * Resources collected by the player. Obviously only contains {@link CardCategory#RESOURCE resource} cards.
@@ -13,7 +19,16 @@ public class Inventory {
      */
     private final List<Item> items = new ArrayList<>();
 
-    public void addResource(Card resourceCard) {
+    /**
+     * Add a resource card to this inventory.
+     *
+     * @param resourceCard resource card
+     * @throws IllegalArgumentException if the provided card is not a resource card
+     */
+    public void addResource(Card resourceCard) throws IllegalArgumentException {
+        if (resourceCard.category() != CardCategory.RESOURCE) {
+            throw new IllegalArgumentException("card is not a resource");
+        }
         resources.add(resourceCard);
     }
 
@@ -37,7 +52,16 @@ public class Inventory {
         }
     }
 
-    public void build(Item item) {
+    /**
+     * Build the specified item.
+     *
+     * @param item item to build
+     * @throws IllegalArgumentException if there are not enough resources to build the item
+     */
+    public void build(Item item) throws IllegalArgumentException {
+        if (!canBuild(item)) {
+            throw new IllegalArgumentException("can not build item");
+        }
         // remove used resources
         for (final Card resource : item.resourcesNeeded()) {
             // resources picked up last get used up first
@@ -46,19 +70,36 @@ public class Inventory {
         items.add(item);
     }
 
+    /**
+     * @return items in the inventory
+     */
     public List<Item> getItems() {
         // have to copy here: caller does not expect an auto-updating list
         return new ArrayList<>(items);
     }
 
+    /**
+     * @return stream of items in the inventory
+     */
     public Stream<Item> itemStream() {
         return items.stream();
     }
 
+    /**
+     * Check whether this inventory contains a specified item.
+     *
+     * @param item single item
+     * @return whether this inventory contains that item
+     */
     public boolean contains(Item item) {
         return items.contains(item);
     }
 
+    /**
+     * Remove an item, if it exists.
+     *
+     * @param item item to remove
+     */
     public void removeItem(Item item) {
         items.remove(item);
     }
@@ -91,6 +132,9 @@ public class Inventory {
         return Arrays.stream(resourcesNeeded).allMatch(Objects::isNull);
     }
 
+    /**
+     * Clear the inventory, deleting all resources and items.
+     */
     public void clear() {
         resources.clear();
         items.clear();
diff --git a/src/edu/kit/informatik/cardgame/ui/CommandLine.java b/src/edu/kit/informatik/cardgame/ui/CommandLine.java
index c654050..63d311d 100644
--- a/src/edu/kit/informatik/cardgame/ui/CommandLine.java
+++ b/src/edu/kit/informatik/cardgame/ui/CommandLine.java
@@ -52,7 +52,7 @@ public final class CommandLine {
                 command = CommandFactory.getCommand(input);
             } catch (NumberFormatException | InvalidInputException e) {
                 Terminal.printError(e.getMessage());
-                continue;
+                continue; // to next command
             }
             // attempt to execute command
             try {
diff --git a/src/edu/kit/informatik/cardgame/ui/command/Command.java b/src/edu/kit/informatik/cardgame/ui/command/Command.java
index 8fe88e2..fc8db9a 100644
--- a/src/edu/kit/informatik/cardgame/ui/command/Command.java
+++ b/src/edu/kit/informatik/cardgame/ui/command/Command.java
@@ -5,7 +5,7 @@ import edu.kit.informatik.cardgame.model.LogicException;
 import edu.kit.informatik.cardgame.ui.InvalidInputException;
 
 /**
- * Command that can be applied to a simulation.
+ * Command that can be applied to a card game.
  * Commands are implemented as separate classes for easy modification and expansion.
  *
  * @author Arne Keller