diff --git a/src/main/resources/application.conf b/src/main/resources/application.conf
index 83e60eb2b..bd8ef92c1 100644
--- a/src/main/resources/application.conf
+++ b/src/main/resources/application.conf
@@ -1510,9 +1510,11 @@ opencomputers {
     # Enable debug card functionality. This may also be of use for custom
     # maps, so it is enabled by default. If you run a server where people
     # may cheat in items but should not have op/admin-like rights, you may
-    # want to set this to false. This will *not* remove the card, it will
-    # just make all functions it provides error out.
-    enableDebugCard: true
+    # want to set this to false or `deny`. Set this to `whitelist` if you
+    # want to enable whitelisting of debug card users (managed by command
+    # /oc_debugWhitelist). This will *not* remove the card, it will just
+    # make all functions it provides error out.
+    debugCardAccess: allow
 
     # Whether to always register the LuaJ architecture - even if the native
     # library is available. In that case it is possible to switch between
diff --git a/src/main/scala/li/cil/oc/Settings.scala b/src/main/scala/li/cil/oc/Settings.scala
index bb38fce98..bd8897fdb 100644
--- a/src/main/scala/li/cil/oc/Settings.scala
+++ b/src/main/scala/li/cil/oc/Settings.scala
@@ -3,6 +3,8 @@ package li.cil.oc
 import java.io._
 import java.net.Inet4Address
 import java.net.InetAddress
+import java.nio.charset.StandardCharsets
+import java.security.SecureRandom
 import java.util.UUID
 
 import com.google.common.net.InetAddresses
@@ -11,11 +13,16 @@ import com.typesafe.config._
 import cpw.mods.fml.common.Loader
 import cpw.mods.fml.common.versioning.DefaultArtifactVersion
 import cpw.mods.fml.common.versioning.VersionRange
+import li.cil.oc.Settings.DebugCardAccess
 import li.cil.oc.common.Tier
 import li.cil.oc.integration.Mods
+import li.cil.oc.server.component.DebugCard
+import li.cil.oc.server.component.DebugCard.AccessContext
+import org.apache.commons.codec.binary.Hex
 import org.apache.commons.lang3.StringEscapeUtils
 
 import scala.collection.convert.WrapAsScala._
+import scala.collection.mutable
 import scala.io.Codec
 import scala.io.Source
 import scala.util.matching.Regex
@@ -413,7 +420,21 @@ class Settings(val config: Config) {
   val nativeInTmpDir = config.getBoolean("debug.nativeInTmpDir")
   val periodicallyForceLightUpdate = config.getBoolean("debug.periodicallyForceLightUpdate")
   val insertIdsInConverters = config.getBoolean("debug.insertIdsInConverters")
-  val enableDebugCard = config.getBoolean("debug.enableDebugCard")
+
+  val debugCardAccess = config.getValue("debug.debugCardAccess").unwrapped() match {
+    case "true" | "allow" | java.lang.Boolean.TRUE => DebugCardAccess.Allowed
+    case "false" | "deny" | java.lang.Boolean.FALSE => DebugCardAccess.Forbidden
+    case "whitelist" =>
+      val wlFile = new File(Loader.instance.getConfigDir + File.separator + "opencomputers" + File.separator +
+                              "debug_card_whitelist.txt")
+
+      DebugCardAccess.Whitelist(wlFile)
+
+    case _ => // Fallback to most secure configuration
+      OpenComputers.log.warn("Unknown debug card access type, falling back to `deny`. Allowed values: `allow`, `deny`, `whitelist`.")
+      DebugCardAccess.Forbidden
+  }
+
   val registerLuaJArchitecture = config.getBoolean("debug.registerLuaJArchitecture")
   val disableLocaleChanging = config.getBoolean("debug.disableLocaleChanging")
 }
@@ -557,4 +578,95 @@ object Settings {
     def apply(inetAddress: InetAddress, host: String) = validator(inetAddress, host)
   }
 
+  sealed trait DebugCardAccess {
+    def checkAccess(ctx: Option[DebugCard.AccessContext]): Option[String]
+  }
+
+  object DebugCardAccess {
+    case object Forbidden extends DebugCardAccess {
+      override def checkAccess(ctx: Option[AccessContext]): Option[String] =
+        Some("debug card is disabled")
+    }
+
+    case object Allowed extends DebugCardAccess {
+      override def checkAccess(ctx: Option[AccessContext]): Option[String] = None
+    }
+
+    case class Whitelist(noncesFile: File) extends DebugCardAccess {
+      private val values = mutable.Map.empty[String, String]
+      private val rng = SecureRandom.getInstance("SHA1PRNG")
+
+      load()
+
+      def save(): Unit = {
+        val noncesDir = noncesFile.getParentFile
+        if (!noncesDir.exists() && !noncesDir.mkdirs())
+          throw new IOException(s"Cannot create nonces directory: ${noncesDir.getCanonicalPath}")
+
+        val writer = new PrintWriter(new OutputStreamWriter(new FileOutputStream(noncesFile), StandardCharsets.UTF_8), false)
+        try {
+          for ((p, n) <- values)
+            writer.println(s"$p $n")
+        } finally writer.close()
+      }
+
+      def load(): Unit = {
+        values.clear()
+
+        if (!noncesFile.exists())
+          return
+
+        val reader = new BufferedReader(new InputStreamReader(new FileInputStream(noncesFile), StandardCharsets.UTF_8))
+        Iterator.continually(reader.readLine())
+          .takeWhile(_ != null)
+          .map(_.split(" ", 2))
+          .flatMap {
+            case Array(p, n) => Seq(p -> n)
+            case _ => Nil
+          }.foreach(values += _)
+      }
+
+      private def generateNonce(): String = {
+        val buf = new Array[Byte](16)
+        rng.nextBytes(buf)
+        new String(Hex.encodeHex(buf, true))
+      }
+
+      def nonce(player: String) = values.get(player.toLowerCase)
+
+      def isWhitelisted(player: String) = values.contains(player.toLowerCase)
+
+      def whitelist: collection.Set[String] = values.keySet
+
+      def add(player: String): Unit = {
+        if (!values.contains(player.toLowerCase)) {
+          values.put(player.toLowerCase, generateNonce())
+          save()
+        }
+      }
+
+      def remove(player: String): Unit = {
+        if (values.remove(player.toLowerCase).isDefined)
+          save()
+      }
+
+      def invalidate(player: String): Unit = {
+        if (values.contains(player.toLowerCase)) {
+          values.put(player.toLowerCase, generateNonce())
+          save()
+        }
+      }
+
+      def checkAccess(ctxOpt: Option[DebugCard.AccessContext]): Option[String] = ctxOpt match {
+        case Some(ctx) => values.get(ctx.player) match {
+          case Some(x) =>
+            if (x == ctx.nonce) None
+            else Some("debug card is invalidated, please re-bind it to yourself")
+          case None => Some("you are not whitelisted to use debug card")
+        }
+
+        case None => Some("debug card is whitelisted, Shift+Click with it to bind card to yourself")
+      }
+    }
+  }
 }
diff --git a/src/main/scala/li/cil/oc/common/item/DebugCard.scala b/src/main/scala/li/cil/oc/common/item/DebugCard.scala
index 837793bbb..7aaf1c669 100644
--- a/src/main/scala/li/cil/oc/common/item/DebugCard.scala
+++ b/src/main/scala/li/cil/oc/common/item/DebugCard.scala
@@ -2,23 +2,41 @@ package li.cil.oc.common.item
 
 import java.util
 
+import li.cil.oc.Settings
+import li.cil.oc.Settings.DebugCardAccess
 import li.cil.oc.common.item.data.DebugCardData
 import net.minecraft.entity.player.EntityPlayer
 import net.minecraft.item.ItemStack
 import net.minecraft.world.World
+import li.cil.oc.server.command.string2text
+import li.cil.oc.server.component.{DebugCard => CDebugCard}
 
 class DebugCard(val parent: Delegator) extends traits.Delegate {
   override protected def tooltipExtended(stack: ItemStack, tooltip: util.List[String]): Unit = {
     super.tooltipExtended(stack, tooltip)
     val data = new DebugCardData(stack)
-    data.player.foreach(name => tooltip.add(s"§8$name§r"))
+    data.access.foreach(access => tooltip.add(s"§8${access.player}§r"))
   }
 
   override def onItemRightClick(stack: ItemStack, world: World, player: EntityPlayer): ItemStack = {
     if (player.isSneaking) {
       val data = new DebugCardData(stack)
-      if (data.player.contains(player.getCommandSenderName)) data.player = None
-      else data.player = Option(player.getCommandSenderName)
+      val name = player.getCommandSenderName
+
+      if (data.access.exists(_.player == name)) data.access = None
+      else data.access =
+        Some(CDebugCard.AccessContext(name, Settings.get.debugCardAccess match {
+          case wl: DebugCardAccess.Whitelist => wl.nonce(name) match {
+            case Some(n) => n
+            case None =>
+              player.addChatComponentMessage("§cYou are not whitelisted to use debug card")
+              player.swingItem()
+              return stack
+          }
+
+          case _ => ""
+        }))
+
       data.save(stack)
       player.swingItem()
     }
diff --git a/src/main/scala/li/cil/oc/common/item/data/DebugCardData.scala b/src/main/scala/li/cil/oc/common/item/data/DebugCardData.scala
index 1b6b339ff..839ef99e2 100644
--- a/src/main/scala/li/cil/oc/common/item/data/DebugCardData.scala
+++ b/src/main/scala/li/cil/oc/common/item/data/DebugCardData.scala
@@ -1,7 +1,7 @@
 package li.cil.oc.common.item.data
 
-import li.cil.oc.Constants
-import li.cil.oc.Settings
+import li.cil.oc.{Constants, Settings}
+import li.cil.oc.server.component.DebugCard.AccessContext
 import net.minecraft.item.ItemStack
 import net.minecraft.nbt.NBTTagCompound
 
@@ -11,19 +11,16 @@ class DebugCardData extends ItemData(Constants.ItemName.DebugCard) {
     load(stack)
   }
 
-  var player: Option[String] = None
+  var access: Option[AccessContext] = None
 
-  override def load(nbt: NBTTagCompound) {
-    val tag = dataTag(nbt)
-    if (tag.hasKey(Settings.namespace + "player")) {
-      player = Option(tag.getString(Settings.namespace + "player"))
-    }
+  override def load(nbt: NBTTagCompound): Unit = {
+    access = AccessContext.load(dataTag(nbt))
   }
 
-  override def save(nbt: NBTTagCompound) {
+  override def save(nbt: NBTTagCompound): Unit = {
     val tag = dataTag(nbt)
-    tag.removeTag(Settings.namespace + "player")
-    player.foreach(tag.setString(Settings.namespace + "player", _))
+    AccessContext.remove(tag)
+    access.foreach(_.save(tag))
   }
 
   private def dataTag(nbt: NBTTagCompound) = {
diff --git a/src/main/scala/li/cil/oc/server/command/CommandHandler.scala b/src/main/scala/li/cil/oc/server/command/CommandHandler.scala
index 0207cc5a1..509e7d3a8 100644
--- a/src/main/scala/li/cil/oc/server/command/CommandHandler.scala
+++ b/src/main/scala/li/cil/oc/server/command/CommandHandler.scala
@@ -10,5 +10,6 @@ object CommandHandler {
     e.registerServerCommand(NonDisassemblyAgreementCommand)
     e.registerServerCommand(WirelessRenderingCommand)
     e.registerServerCommand(SpawnComputerCommand)
+    e.registerServerCommand(DebugWhitelistCommand)
   }
 }
diff --git a/src/main/scala/li/cil/oc/server/command/DebugWhitelistCommand.scala b/src/main/scala/li/cil/oc/server/command/DebugWhitelistCommand.scala
new file mode 100644
index 000000000..0bf8305d9
--- /dev/null
+++ b/src/main/scala/li/cil/oc/server/command/DebugWhitelistCommand.scala
@@ -0,0 +1,52 @@
+package li.cil.oc.server.command
+
+import li.cil.oc.Settings
+import li.cil.oc.Settings.DebugCardAccess
+import li.cil.oc.common.command.SimpleCommand
+import net.minecraft.command.{ICommandSender, WrongUsageException}
+
+object DebugWhitelistCommand extends SimpleCommand("oc_debugWhitelist") {
+  // Required OP levels:
+  //  to revoke your cards - 0
+  //  to do other whitelist manipulation - 2
+
+  override def getRequiredPermissionLevel = 0
+  private def isOp(sender: ICommandSender) = getOpLevel(sender) >= 2
+
+  override def getCommandUsage(sender: ICommandSender): String =
+    if (isOp(sender)) name + " [revoke|add|remove] <player> OR " + name + " [revoke|list]"
+    else name + " revoke"
+
+  override def processCommand(sender: ICommandSender, args: Array[String]): Unit = {
+    val wl = Settings.get.debugCardAccess match {
+      case w: DebugCardAccess.Whitelist => w
+      case _ => throw new WrongUsageException("§cDebug card whitelisting is not enabled.")
+    }
+
+    def revokeUser(player: String): Unit = {
+      if (wl.isWhitelisted(player)) {
+        wl.invalidate(player)
+        sender.addChatMessage("§aAll your debug cards were invalidated.")
+      } else sender.addChatMessage("§cYou are not whitelisted to use debug card.")
+    }
+
+    args match {
+      case Array("revoke") => revokeUser(sender.getCommandSenderName)
+      case Array("revoke", player) if isOp(sender) => revokeUser(player)
+      case Array("list") if isOp(sender) =>
+        val players = wl.whitelist
+        if (players.nonEmpty)
+          sender.addChatMessage("§aCurrently whitelisted players: §e" + players.mkString(", "))
+        else
+          sender.addChatMessage("§cThere is no currently whitelisted players.")
+      case Array("add", player) if isOp(sender) =>
+        wl.add(player)
+        sender.addChatMessage("§aPlayer was added to whitelist.")
+      case Array("remove", player) if isOp(sender) =>
+        wl.remove(player)
+        sender.addChatMessage("§aPlayer was removed from whitelist")
+      case _ =>
+        sender.addChatMessage("§e" + getCommandUsage(sender))
+    }
+  }
+}
diff --git a/src/main/scala/li/cil/oc/server/command/package.scala b/src/main/scala/li/cil/oc/server/command/package.scala
new file mode 100644
index 000000000..304ca02d3
--- /dev/null
+++ b/src/main/scala/li/cil/oc/server/command/package.scala
@@ -0,0 +1,32 @@
+package li.cil.oc.server
+
+import java.util.logging.Level
+
+import cpw.mods.fml.common.FMLLog
+import net.minecraft.command.ICommandSender
+import net.minecraft.entity.player.EntityPlayerMP
+import net.minecraft.server.MinecraftServer
+import net.minecraft.server.management.UserListOpsEntry
+import net.minecraft.util.{ChatComponentText, IChatComponent}
+
+import scala.language.implicitConversions
+
+package object command {
+  implicit def string2text(s: String): IChatComponent = new ChatComponentText(s)
+
+  def getOpLevel(sender: ICommandSender): Int = {
+    // Shitty minecraft server logic & shitty minecraft server code.
+    val srv = MinecraftServer.getServer
+    if (srv.isSinglePlayer && srv.worldServers.head.getWorldInfo.areCommandsAllowed &&
+      srv.getServerOwner.equalsIgnoreCase(sender.getCommandSenderName) /* || srv.commandsAllowedForAll */ )
+      return 4
+
+    sender match {
+      case _: MinecraftServer => 4
+      case p: EntityPlayerMP =>
+        val e = srv.getConfigurationManager.func_152603_m.func_152683_b(p.getGameProfile)
+        if (e == null) 0 else e.asInstanceOf[UserListOpsEntry].func_152644_a()
+      case _ => 0
+    }
+  }
+}
diff --git a/src/main/scala/li/cil/oc/server/component/DebugCard.scala b/src/main/scala/li/cil/oc/server/component/DebugCard.scala
index fd5b71965..99ade4b53 100644
--- a/src/main/scala/li/cil/oc/server/component/DebugCard.scala
+++ b/src/main/scala/li/cil/oc/server/component/DebugCard.scala
@@ -16,7 +16,7 @@ import li.cil.oc.api.network.SidedEnvironment
 import li.cil.oc.api.network.Visibility
 import li.cil.oc.api.prefab
 import li.cil.oc.api.prefab.AbstractValue
-import li.cil.oc.server.component.DebugCard.CommandSender
+import li.cil.oc.server.component.DebugCard.{AccessContext, CommandSender}
 import li.cil.oc.util.BlockPosition
 import li.cil.oc.util.ExtendedArguments._
 import li.cil.oc.util.ExtendedNBT._
@@ -57,7 +57,9 @@ class DebugCard(host: EnvironmentHost) extends prefab.ManagedEnvironment {
   private var remoteNodePosition: Option[(Int, Int, Int)] = None
 
   // Player this card is bound to (if any) to use for permissions.
-  var player: Option[String] = None
+  implicit var access: Option[AccessContext] = None
+
+  def player = access.map(_.player)
 
   private lazy val CommandSender = {
     def defaultFakePlayer = FakePlayerFactory.get(host.world.asInstanceOf[WorldServer], Settings.get.fakePlayerProfile)
@@ -72,67 +74,67 @@ class DebugCard(host: EnvironmentHost) extends prefab.ManagedEnvironment {
 
   // ----------------------------------------------------------------------- //
 
-  import li.cil.oc.server.component.DebugCard.checkEnabled
+  import li.cil.oc.server.component.DebugCard.checkAccess
 
   @Callback(doc = """function(value:number):number -- Changes the component network's energy buffer by the specified delta.""")
   def changeBuffer(context: Context, args: Arguments): Array[AnyRef] = {
-    checkEnabled()
+    checkAccess()
     result(node.changeBuffer(args.checkDouble(0)))
   }
 
   @Callback(doc = """function():number -- Get the container's X position in the world.""")
   def getX(context: Context, args: Arguments): Array[AnyRef] = {
-    checkEnabled()
+    checkAccess()
     result(host.xPosition)
   }
 
   @Callback(doc = """function():number -- Get the container's Y position in the world.""")
   def getY(context: Context, args: Arguments): Array[AnyRef] = {
-    checkEnabled()
+    checkAccess()
     result(host.yPosition)
   }
 
   @Callback(doc = """function():number -- Get the container's Z position in the world.""")
   def getZ(context: Context, args: Arguments): Array[AnyRef] = {
-    checkEnabled()
+    checkAccess()
     result(host.zPosition)
   }
 
   @Callback(doc = """function([id:number]):userdata -- Get the world object for the specified dimension ID, or the container's.""")
   def getWorld(context: Context, args: Arguments): Array[AnyRef] = {
-    checkEnabled()
+    checkAccess()
     if (args.count() > 0) result(new DebugCard.WorldValue(DimensionManager.getWorld(args.checkInteger(0))))
     else result(new DebugCard.WorldValue(host.world))
   }
 
   @Callback(doc = """function():table -- Get a list of all world IDs, loaded and unloaded.""")
   def getWorlds(context: Context, args: Arguments): Array[AnyRef] = {
-    checkEnabled()
+    checkAccess()
     result(DimensionManager.getStaticDimensionIDs)
   }
 
   @Callback(doc = """function(name:string):userdata -- Get the entity of a player.""")
   def getPlayer(context: Context, args: Arguments): Array[AnyRef] = {
-    checkEnabled()
+    checkAccess()
     result(new DebugCard.PlayerValue(args.checkString(0)))
   }
 
   @Callback(doc = """function():table -- Get a list of currently logged-in players.""")
   def getPlayers(context: Context, args: Arguments): Array[AnyRef] = {
-    checkEnabled()
+    checkAccess()
     result(MinecraftServer.getServer.getAllUsernames)
   }
 
   @Callback(doc = """function(name:string):boolean -- Get whether a mod or API is loaded.""")
   def isModLoaded(context: Context, args: Arguments): Array[AnyRef] = {
-    checkEnabled()
+    checkAccess()
     val name = args.checkString(0)
     result(Loader.isModLoaded(name) || ModAPIManager.INSTANCE.hasAPI(name))
   }
 
   @Callback(doc = """function(command:string):number -- Runs an arbitrary command using a fake player.""")
   def runCommand(context: Context, args: Arguments): Array[AnyRef] = {
-    checkEnabled()
+    checkAccess()
     val commands =
       if (args.isTable(0)) collectionAsScalaIterable(args.checkTable(0).values())
       else Iterable(args.checkString(0))
@@ -149,7 +151,7 @@ class DebugCard(host: EnvironmentHost) extends prefab.ManagedEnvironment {
 
   @Callback(doc = """function(x:number, y:number, z:number):boolean -- Connect the debug card to the block at the specified coordinates.""")
   def connectToBlock(context: Context, args: Arguments): Array[AnyRef] = {
-    checkEnabled()
+    checkAccess()
     val x = args.checkInteger(0)
     val y = args.checkInteger(1)
     val z = args.checkInteger(2)
@@ -177,7 +179,7 @@ class DebugCard(host: EnvironmentHost) extends prefab.ManagedEnvironment {
 
   @Callback(doc = """function():userdata -- Test method for user-data and general value conversion.""")
   def test(context: Context, args: Arguments): Array[AnyRef] = {
-    checkEnabled()
+    checkAccess()
 
     val v1 = mutable.Map("a" -> true, "b" -> "test")
     val v2 = Map(10 -> "zxc", false -> v1)
@@ -215,42 +217,63 @@ class DebugCard(host: EnvironmentHost) extends prefab.ManagedEnvironment {
 
   override def load(nbt: NBTTagCompound): Unit = {
     super.load(nbt)
+    access = AccessContext.load(nbt)
     if (nbt.hasKey(Settings.namespace + "remoteX")) {
       val x = nbt.getInteger(Settings.namespace + "remoteX")
       val y = nbt.getInteger(Settings.namespace + "remoteY")
       val z = nbt.getInteger(Settings.namespace + "remoteZ")
       remoteNodePosition = Some((x, y, z))
     }
-    if (nbt.hasKey(Settings.namespace + "player")) {
-      player = Option(nbt.getString(Settings.namespace + "player"))
-    }
   }
 
   override def save(nbt: NBTTagCompound): Unit = {
     super.save(nbt)
+    access.foreach(_.save(nbt))
     remoteNodePosition.foreach {
       case (x, y, z) =>
         nbt.setInteger(Settings.namespace + "remoteX", x)
         nbt.setInteger(Settings.namespace + "remoteY", y)
         nbt.setInteger(Settings.namespace + "remoteZ", z)
     }
-    player.foreach(nbt.setString(Settings.namespace + "player", _))
   }
 }
 
 object DebugCard {
+  def checkAccess()(implicit ctx: Option[AccessContext]) =
+    for (msg <- Settings.get.debugCardAccess.checkAccess(ctx))
+      throw new Exception(msg)
 
-  import li.cil.oc.util.ResultWrapper.result
+  object AccessContext {
+    def remove(nbt: NBTTagCompound): Unit = {
+      nbt.removeTag(Settings.namespace + "player")
+      nbt.removeTag(Settings.namespace + "accessNonce")
+    }
 
-  def checkEnabled() = if (!Settings.get.enableDebugCard) throw new Exception("debug card functionality is disabled")
+    def load(nbt: NBTTagCompound): Option[AccessContext] = {
+      if (nbt.hasKey(Settings.namespace + "player"))
+        Some(AccessContext(
+          nbt.getString(Settings.namespace + "player"),
+          nbt.getString(Settings.namespace + "accessNonce")
+        ))
+      else
+        None
+    }
+  }
 
-  class PlayerValue(var name: String) extends prefab.AbstractValue {
-    def this() = this("") // For loading.
+  case class AccessContext(player: String, nonce: String) {
+    def save(nbt: NBTTagCompound): Unit = {
+      nbt.setString(Settings.namespace + "player", player)
+      nbt.setString(Settings.namespace + "accessNonce", nonce)
+    }
+  }
+
+  class PlayerValue(var name: String)(implicit var ctx: Option[AccessContext]) extends prefab.AbstractValue {
+    def this() = this("")(None) // For loading.
 
     // ----------------------------------------------------------------------- //
 
     def withPlayer(f: (EntityPlayerMP) => Array[AnyRef]) = {
-      checkEnabled()
+      checkAccess()
       MinecraftServer.getServer.getConfigurationManager.func_152612_a(name) match {
         case player: EntityPlayerMP => f(player)
         case _ => result(Unit, "player is offline")
@@ -304,93 +327,95 @@ object DebugCard {
 
     override def load(nbt: NBTTagCompound) {
       super.load(nbt)
+      ctx = AccessContext.load(nbt)
       name = nbt.getString("name")
     }
 
     override def save(nbt: NBTTagCompound) {
       super.save(nbt)
+      ctx.foreach(_.save(nbt))
       nbt.setString("name", name)
     }
   }
 
-  class WorldValue(var world: World) extends prefab.AbstractValue {
-    def this() = this(null) // For loading.
+  class WorldValue(var world: World)(implicit var ctx: Option[AccessContext]) extends prefab.AbstractValue {
+    def this() = this(null)(None) // For loading.
 
     // ----------------------------------------------------------------------- //
 
     @Callback(doc = """function():number -- Gets the numeric id of the current dimension.""")
     def getDimensionId(context: Context, args: Arguments): Array[AnyRef] = {
-      checkEnabled()
+      checkAccess()
       result(world.provider.dimensionId)
     }
 
     @Callback(doc = """function():string -- Gets the name of the current dimension.""")
     def getDimensionName(context: Context, args: Arguments): Array[AnyRef] = {
-      checkEnabled()
+      checkAccess()
       result(world.provider.getDimensionName)
     }
 
     @Callback(doc = """function():number -- Gets the seed of the world.""")
     def getSeed(context: Context, args: Arguments): Array[AnyRef] = {
-      checkEnabled()
+      checkAccess()
       result(world.getSeed)
     }
 
     @Callback(doc = """function():boolean -- Returns whether it is currently raining.""")
     def isRaining(context: Context, args: Arguments): Array[AnyRef] = {
-      checkEnabled()
+      checkAccess()
       result(world.isRaining)
     }
 
     @Callback(doc = """function(value:boolean) -- Sets whether it is currently raining.""")
     def setRaining(context: Context, args: Arguments): Array[AnyRef] = {
-      checkEnabled()
+      checkAccess()
       world.getWorldInfo.setRaining(args.checkBoolean(0))
       null
     }
 
     @Callback(doc = """function():boolean -- Returns whether it is currently thundering.""")
     def isThundering(context: Context, args: Arguments): Array[AnyRef] = {
-      checkEnabled()
+      checkAccess()
       result(world.isThundering)
     }
 
     @Callback(doc = """function(value:boolean) -- Sets whether it is currently thundering.""")
     def setThundering(context: Context, args: Arguments): Array[AnyRef] = {
-      checkEnabled()
+      checkAccess()
       world.getWorldInfo.setThundering(args.checkBoolean(0))
       null
     }
 
     @Callback(doc = """function():number -- Get the current world time.""")
     def getTime(context: Context, args: Arguments): Array[AnyRef] = {
-      checkEnabled()
+      checkAccess()
       result(world.getWorldTime)
     }
 
     @Callback(doc = """function(value:number) -- Set the current world time.""")
     def setTime(context: Context, args: Arguments): Array[AnyRef] = {
-      checkEnabled()
+      checkAccess()
       world.setWorldTime(args.checkDouble(0).toLong)
       null
     }
 
     @Callback(doc = """function():number, number, number -- Get the current spawn point coordinates.""")
     def getSpawnPoint(context: Context, args: Arguments): Array[AnyRef] = {
-      checkEnabled()
+      checkAccess()
       result(world.getWorldInfo.getSpawnX, world.getWorldInfo.getSpawnY, world.getWorldInfo.getSpawnZ)
     }
 
     @Callback(doc = """function(x:number, y:number, z:number) -- Set the spawn point coordinates.""")
     def setSpawnPoint(context: Context, args: Arguments): Array[AnyRef] = {
-      checkEnabled()
+      checkAccess()
       world.getWorldInfo.setSpawnPosition(args.checkInteger(0), args.checkInteger(1), args.checkInteger(2))
       null
     }
 
     @Callback(doc = """function(x:number, y:number, z:number, sound:string, range:number) -- Play a sound at the specified coordinates.""")
     def playSoundAt(context: Context, args: Arguments): Array[AnyRef] = {
-      checkEnabled()
+      checkAccess()
       val (x, y, z) = (args.checkInteger(0), args.checkInteger(1), args.checkInteger(2))
       val sound = args.checkString(3)
       val range = args.checkInteger(4)
@@ -402,25 +427,25 @@ object DebugCard {
 
     @Callback(doc = """function(x:number, y:number, z:number):number -- Get the ID of the block at the specified coordinates.""")
     def getBlockId(context: Context, args: Arguments): Array[AnyRef] = {
-      checkEnabled()
+      checkAccess()
       result(Block.getIdFromBlock(world.getBlock(args.checkInteger(0), args.checkInteger(1), args.checkInteger(2))))
     }
 
     @Callback(doc = """function(x:number, y:number, z:number):number -- Get the metadata of the block at the specified coordinates.""")
     def getMetadata(context: Context, args: Arguments): Array[AnyRef] = {
-      checkEnabled()
+      checkAccess()
       result(world.getBlockMetadata(args.checkInteger(0), args.checkInteger(1), args.checkInteger(2)))
     }
 
     @Callback(doc = """function(x:number, y:number, z:number):number -- Check whether the block at the specified coordinates is loaded.""")
     def isLoaded(context: Context, args: Arguments): Array[AnyRef] = {
-      checkEnabled()
+      checkAccess()
       result(world.blockExists(args.checkInteger(0), args.checkInteger(1), args.checkInteger(2)))
     }
 
     @Callback(doc = """function(x:number, y:number, z:number):number -- Check whether the block at the specified coordinates has a tile entity.""")
     def hasTileEntity(context: Context, args: Arguments): Array[AnyRef] = {
-      checkEnabled()
+      checkAccess()
       val (x, y, z) = (args.checkInteger(0), args.checkInteger(1), args.checkInteger(2))
       val block = world.getBlock(x, y, z)
       result(block != null && block.hasTileEntity(world.getBlockMetadata(x, y, z)))
@@ -428,7 +453,7 @@ object DebugCard {
 
     @Callback(doc = """function(x:number, y:number, z:number):table -- Get the NBT of the block at the specified coordinates.""")
     def getTileNBT(context: Context, args: Arguments): Array[AnyRef] = {
-      checkEnabled()
+      checkAccess()
       val (x, y, z) = (args.checkInteger(0), args.checkInteger(1), args.checkInteger(2))
       world.getTileEntity(x, y, z) match {
         case tileEntity: TileEntity => result(toNbt(tileEntity.writeToNBT _).toTypedMap)
@@ -438,7 +463,7 @@ object DebugCard {
 
     @Callback(doc = """function(x:number, y:number, z:number, nbt:table):boolean -- Set the NBT of the block at the specified coordinates.""")
     def setTileNBT(context: Context, args: Arguments): Array[AnyRef] = {
-      checkEnabled()
+      checkAccess()
       val (x, y, z) = (args.checkInteger(0), args.checkInteger(1), args.checkInteger(2))
       world.getTileEntity(x, y, z) match {
         case tileEntity: TileEntity =>
@@ -456,25 +481,25 @@ object DebugCard {
 
     @Callback(doc = """function(x:number, y:number, z:number):number -- Get the light opacity of the block at the specified coordinates.""")
     def getLightOpacity(context: Context, args: Arguments): Array[AnyRef] = {
-      checkEnabled()
+      checkAccess()
       result(world.getBlockLightOpacity(args.checkInteger(0), args.checkInteger(1), args.checkInteger(2)))
     }
 
     @Callback(doc = """function(x:number, y:number, z:number):number -- Get the light value (emission) of the block at the specified coordinates.""")
     def getLightValue(context: Context, args: Arguments): Array[AnyRef] = {
-      checkEnabled()
+      checkAccess()
       result(world.getBlockLightValue(args.checkInteger(0), args.checkInteger(1), args.checkInteger(2)))
     }
 
     @Callback(doc = """function(x:number, y:number, z:number):number -- Get whether the block at the specified coordinates is directly under the sky.""")
     def canSeeSky(context: Context, args: Arguments): Array[AnyRef] = {
-      checkEnabled()
+      checkAccess()
       result(world.canBlockSeeTheSky(args.checkInteger(0), args.checkInteger(1), args.checkInteger(2)))
     }
 
     @Callback(doc = """function(x:number, y:number, z:number, id:number or string, meta:number):number -- Set the block at the specified coordinates.""")
     def setBlock(context: Context, args: Arguments): Array[AnyRef] = {
-      checkEnabled()
+      checkAccess()
       val block = if (args.isInteger(3)) Block.getBlockById(args.checkInteger(3)) else Block.getBlockFromName(args.checkString(3))
       val metadata = args.checkInteger(4)
       result(world.setBlock(args.checkInteger(0), args.checkInteger(1), args.checkInteger(2), block, metadata, 3))
@@ -482,7 +507,7 @@ object DebugCard {
 
     @Callback(doc = """function(x1:number, y1:number, z1:number, x2:number, y2:number, z2:number, id:number or string, meta:number):number -- Set all blocks in the area defined by the two corner points (x1, y1, z1) and (x2, y2, z2).""")
     def setBlocks(context: Context, args: Arguments): Array[AnyRef] = {
-      checkEnabled()
+      checkAccess()
       val (xMin, yMin, zMin) = (args.checkInteger(0), args.checkInteger(1), args.checkInteger(2))
       val (xMax, yMax, zMax) = (args.checkInteger(3), args.checkInteger(4), args.checkInteger(5))
       val block = if (args.isInteger(6)) Block.getBlockById(args.checkInteger(6)) else Block.getBlockFromName(args.checkString(6))
@@ -501,7 +526,7 @@ object DebugCard {
 
     @Callback(doc = """function(id:string, count:number, damage:number, nbt:string, x:number, y:number, z:number, side:number):boolean - Insert an item stack into the inventory at the specified location. NBT tag is expected in JSON format.""")
     def insertItem(context: Context, args: Arguments): Array[AnyRef] = {
-      checkEnabled()
+      checkAccess()
       val item = Item.itemRegistry.getObject(args.checkString(0)).asInstanceOf[Item]
       if (item == null) {
         throw new IllegalArgumentException("invalid item id")
@@ -523,7 +548,7 @@ object DebugCard {
 
     @Callback(doc = """function(x:number, y:number, z:number, slot:number[, count:number]):number - Reduce the size of an item stack in the inventory at the specified location.""")
     def removeItem(context: Context, args: Arguments): Array[AnyRef] = {
-      checkEnabled()
+      checkAccess()
       val position = BlockPosition(args.checkDouble(0), args.checkDouble(1), args.checkDouble(2), world)
       InventoryUtils.inventoryAt(position) match {
         case Some(inventory) =>
@@ -538,7 +563,7 @@ object DebugCard {
 
     @Callback(doc = """function(id:string, amount:number, x:number, y:number, z:number, side:number):boolean - Insert some fluid into the tank at the specified location.""")
     def insertFluid(context: Context, args: Arguments): Array[AnyRef] = {
-      checkEnabled()
+      checkAccess()
       val fluid = FluidRegistry.getFluid(args.checkString(0))
       if (fluid == null) {
         throw new IllegalArgumentException("invalid fluid id")
@@ -554,7 +579,7 @@ object DebugCard {
 
     @Callback(doc = """function(amount:number, x:number, y:number, z:number, side:number):boolean - Remove some fluid from a tank at the specified location.""")
     def removeFluid(context: Context, args: Arguments): Array[AnyRef] = {
-      checkEnabled()
+      checkAccess()
       val amount = args.checkInteger(0)
       val position = BlockPosition(args.checkDouble(1), args.checkDouble(2), args.checkDouble(3), world)
       val side = args.checkSideAny(4)
@@ -568,11 +593,13 @@ object DebugCard {
 
     override def load(nbt: NBTTagCompound) {
       super.load(nbt)
+      ctx = AccessContext.load(nbt)
       world = DimensionManager.getWorld(nbt.getInteger("dimension"))
     }
 
     override def save(nbt: NBTTagCompound) {
       super.save(nbt)
+      ctx.foreach(_.save(nbt))
       nbt.setInteger("dimension", world.provider.dimensionId)
     }
   }