diff --git a/.idea/libraries/kotlin_annotations_ext.xml b/.idea/libraries/kotlin_annotations_ext.xml
new file mode 100644
index 00000000000..5d04b2a1c30
--- /dev/null
+++ b/.idea/libraries/kotlin_annotations_ext.xml
@@ -0,0 +1,9 @@
+<component name="libraryTable">
+  <library name="kotlin-annotations-ext">
+    <CLASSES>
+      <root url="jar://$KOTLIN_BUNDLED$/lib/kotlin-annotations-ext.jar!/" />
+    </CLASSES>
+    <JAVADOC />
+    <SOURCES />
+  </library>
+</component>
\ No newline at end of file
diff --git a/build.xml b/build.xml
index cc2e2688e24..5a7146685ff 100644
--- a/build.xml
+++ b/build.xml
@@ -12,6 +12,7 @@
     <property name="bootstrap.home" value="dependencies/bootstrap-compiler"/>
     <property name="bootstrap.compiler.home" value="${bootstrap.home}/Kotlin/kotlinc"/>
     <property name="bootstrap.runtime" value="${bootstrap.compiler.home}/lib/kotlin-runtime.jar"/>
+    <property name="bootstrap.annotations.ext" value="${bootstrap.compiler.home}/lib/kotlin-annotations-ext.jar"/>
 
     <property name="output.relative" value="dist"/>
     <property name="output" value="${basedir}/${output.relative}"/>
@@ -28,6 +29,7 @@
 
     <path id="classpath">
         <file file="${bootstrap.runtime}"/>
+        <file file="${bootstrap.annotations.ext}"/>
         <fileset dir="${idea.sdk}" includes="core/*.jar"/>
         <fileset dir="${idea.sdk}" includes="lib/protobuf-2.5.0.jar"/>
 
@@ -375,6 +377,7 @@
 
                     -libraryjars '${rtjar}'
                     -libraryjars '${bootstrap.runtime}'
+                    -libraryjars '${bootstrap.annotations.ext}'
 
                     -target 1.6
                     -dontoptimize
diff --git a/core/descriptors/descriptors.iml b/core/descriptors/descriptors.iml
index bbd44fe9e51..5b73f2110a0 100644
--- a/core/descriptors/descriptors.iml
+++ b/core/descriptors/descriptors.iml
@@ -10,6 +10,7 @@
     <orderEntry type="library" scope="PROVIDED" name="intellij-core" level="project" />
     <orderEntry type="module" module-name="util.runtime" />
     <orderEntry type="module" module-name="serialization" />
+    <orderEntry type="library" name="kotlin-annotations-ext" level="project" />
   </component>
 </module>
 
diff --git a/core/descriptors/src/org/jetbrains/jet/lang/descriptors/ClassDescriptor.java b/core/descriptors/src/org/jetbrains/jet/lang/descriptors/ClassDescriptor.java
index 1aee6cdb6a2..ff2e14dcaf4 100644
--- a/core/descriptors/src/org/jetbrains/jet/lang/descriptors/ClassDescriptor.java
+++ b/core/descriptors/src/org/jetbrains/jet/lang/descriptors/ClassDescriptor.java
@@ -18,6 +18,7 @@ package org.jetbrains.jet.lang.descriptors;
 
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
+import org.jetbrains.annotations.ReadOnly;
 import org.jetbrains.jet.lang.resolve.scopes.JetScope;
 import org.jetbrains.jet.lang.types.JetType;
 import org.jetbrains.jet.lang.types.TypeProjection;
@@ -35,6 +36,7 @@ public interface ClassDescriptor extends ClassifierDescriptor, MemberDescriptor,
     JetScope getUnsubstitutedInnerClassesScope();
 
     @NotNull
+    @ReadOnly
     Collection<ConstructorDescriptor> getConstructors();
 
     @Override
diff --git a/core/descriptors/src/org/jetbrains/jet/lang/descriptors/annotations/Annotated.java b/core/descriptors/src/org/jetbrains/jet/lang/descriptors/annotations/Annotated.java
index 7c1bcc6da88..cabbf3c9f3b 100644
--- a/core/descriptors/src/org/jetbrains/jet/lang/descriptors/annotations/Annotated.java
+++ b/core/descriptors/src/org/jetbrains/jet/lang/descriptors/annotations/Annotated.java
@@ -16,8 +16,11 @@
 
 package org.jetbrains.jet.lang.descriptors.annotations;
 
+import org.jetbrains.annotations.ReadOnly;
+
 import java.util.List;
 
 public interface Annotated {
+    @ReadOnly
     List<AnnotationDescriptor> getAnnotations();
 }
diff --git a/core/descriptors/src/org/jetbrains/jet/lang/descriptors/impl/AbstractLazyTypeParameterDescriptor.java b/core/descriptors/src/org/jetbrains/jet/lang/descriptors/impl/AbstractLazyTypeParameterDescriptor.java
index bc362bd2732..f08ef908ec1 100644
--- a/core/descriptors/src/org/jetbrains/jet/lang/descriptors/impl/AbstractLazyTypeParameterDescriptor.java
+++ b/core/descriptors/src/org/jetbrains/jet/lang/descriptors/impl/AbstractLazyTypeParameterDescriptor.java
@@ -18,6 +18,7 @@ package org.jetbrains.jet.lang.descriptors.impl;
 
 import jet.Function0;
 import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.ReadOnly;
 import org.jetbrains.jet.lang.descriptors.ClassifierDescriptor;
 import org.jetbrains.jet.lang.descriptors.DeclarationDescriptor;
 import org.jetbrains.jet.lang.descriptors.DeclarationDescriptorVisitor;
@@ -109,6 +110,7 @@ public abstract class AbstractLazyTypeParameterDescriptor implements TypeParamet
     }
 
     @NotNull
+    @ReadOnly
     protected abstract Set<JetType> resolveUpperBounds();
 
     @NotNull
diff --git a/core/descriptors/src/org/jetbrains/jet/lang/resolve/scopes/JetScope.java b/core/descriptors/src/org/jetbrains/jet/lang/resolve/scopes/JetScope.java
index 31e4d09af99..bbc6064cf3f 100644
--- a/core/descriptors/src/org/jetbrains/jet/lang/resolve/scopes/JetScope.java
+++ b/core/descriptors/src/org/jetbrains/jet/lang/resolve/scopes/JetScope.java
@@ -18,6 +18,7 @@ package org.jetbrains.jet.lang.resolve.scopes;
 
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
+import org.jetbrains.annotations.ReadOnly;
 import org.jetbrains.jet.lang.descriptors.*;
 import org.jetbrains.jet.lang.resolve.name.LabelName;
 import org.jetbrains.jet.lang.resolve.name.Name;
@@ -49,24 +50,28 @@ public interface JetScope {
     ClassDescriptor getObjectDescriptor(@NotNull Name name);
 
     @NotNull
+    @ReadOnly
     Collection<ClassDescriptor> getObjectDescriptors();
 
     @Nullable
     NamespaceDescriptor getNamespace(@NotNull Name name);
 
     @NotNull
+    @ReadOnly
     Collection<VariableDescriptor> getProperties(@NotNull Name name);
 
     @Nullable
     VariableDescriptor getLocalVariable(@NotNull Name name);
 
     @NotNull
+    @ReadOnly
     Collection<FunctionDescriptor> getFunctions(@NotNull Name name);
 
     @NotNull
     DeclarationDescriptor getContainingDeclaration();
 
     @NotNull
+    @ReadOnly
     Collection<DeclarationDescriptor> getDeclarationsByLabel(@NotNull LabelName labelName);
 
     /**
@@ -75,14 +80,17 @@ public interface JetScope {
      * @return All visible descriptors from current scope.
      */
     @NotNull
+    @ReadOnly
     Collection<DeclarationDescriptor> getAllDescriptors();
 
     /**
      * Adds receivers to the list in order of locality, so that the closest (the most local) receiver goes first
      */
     @NotNull
+    @ReadOnly
     List<ReceiverParameterDescriptor> getImplicitReceiversHierarchy();
 
     @NotNull
+    @ReadOnly
     Collection<DeclarationDescriptor> getOwnDeclaredDescriptors();
 }
diff --git a/core/descriptors/src/org/jetbrains/jet/lang/types/JetType.java b/core/descriptors/src/org/jetbrains/jet/lang/types/JetType.java
index fd56e2375e2..2b7f96b1196 100644
--- a/core/descriptors/src/org/jetbrains/jet/lang/types/JetType.java
+++ b/core/descriptors/src/org/jetbrains/jet/lang/types/JetType.java
@@ -17,6 +17,7 @@
 package org.jetbrains.jet.lang.types;
 
 import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.ReadOnly;
 import org.jetbrains.jet.lang.descriptors.annotations.Annotated;
 import org.jetbrains.jet.lang.resolve.scopes.JetScope;
 import org.jetbrains.jet.lang.types.checker.JetTypeChecker;
@@ -29,7 +30,9 @@ import java.util.List;
 public interface JetType extends Annotated {
     @NotNull TypeConstructor getConstructor();
 
-    @NotNull List<TypeProjection> getArguments();
+    @NotNull
+    @ReadOnly
+    List<TypeProjection> getArguments();
 
     boolean isNullable();
 
diff --git a/core/descriptors/src/org/jetbrains/jet/lang/types/TypeConstructor.java b/core/descriptors/src/org/jetbrains/jet/lang/types/TypeConstructor.java
index 8615b11164b..9abb487aaf7 100644
--- a/core/descriptors/src/org/jetbrains/jet/lang/types/TypeConstructor.java
+++ b/core/descriptors/src/org/jetbrains/jet/lang/types/TypeConstructor.java
@@ -18,6 +18,7 @@ package org.jetbrains.jet.lang.types;
 
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
+import org.jetbrains.annotations.ReadOnly;
 import org.jetbrains.jet.lang.descriptors.ClassifierDescriptor;
 import org.jetbrains.jet.lang.descriptors.TypeParameterDescriptor;
 import org.jetbrains.jet.lang.descriptors.annotations.Annotated;
@@ -27,9 +28,11 @@ import java.util.List;
 
 public interface TypeConstructor extends Annotated {
     @NotNull
+    @ReadOnly
     List<TypeParameterDescriptor> getParameters();
 
     @NotNull
+    @ReadOnly
     Collection<JetType> getSupertypes();
 
     /**