diff --git a/build.gradle.kts b/build.gradle.kts
index 6ce33aa..2e3eab6 100644
--- a/build.gradle.kts
+++ b/build.gradle.kts
@@ -68,7 +68,7 @@ intellij {
 		.mapNotNull { fromToolbox(root, it) }.firstOrNull()
 	pycharmPath?.absolutePath?.let { alternativeIdePath = it }
 
-	setPlugins("PsiViewer:192-SNAPSHOT")
+	setPlugins("PsiViewer:191.4212")
 }
 
 java {
diff --git a/res/META-INF/change-notes.html b/res/META-INF/change-notes.html
index a215a99..c33e0fc 100644
--- a/res/META-INF/change-notes.html
+++ b/res/META-INF/change-notes.html
@@ -2,6 +2,7 @@
 <ul>
 	<li>IntelliJ Platform 2019.2 compatibility</li>
 	<li>Tons of internal refactorings: generate more codes</li>
+	<li>CubicalTT folding</li>
 </ul>
 0.4.2<br/>
 <ul>
diff --git a/res/META-INF/description.html b/res/META-INF/description.html
index 9bc36e8..aec923f 100644
--- a/res/META-INF/description.html
+++ b/res/META-INF/description.html
@@ -84,6 +84,7 @@ <h3>Features (listed for each supported language):</h3><br/>
 			<li>Running (type checking) your code</li>
 			<li>Live template contexts</li>
 			<li>Executable (cubical) management</li>
+			<li>Folding code blocks and imports</li>
 			<li>Syntax highlighter, color settings page</li>
 			<li>Completion/find usages/goto declaration</li>
 			<li>Stub indices, goto symbol (search everywhere)</li>
diff --git a/res/META-INF/plugin.xml b/res/META-INF/plugin.xml
index 08cf761..ba894d9 100644
--- a/res/META-INF/plugin.xml
+++ b/res/META-INF/plugin.xml
@@ -64,6 +64,7 @@
 		<lang.findUsagesProvider language="CubicalTT" implementationClass="org.ice1000.tt.editing.cubicaltt.CubicalTTFindUsagesProvider"/>
 		<lang.syntaxHighlighterFactory language="CubicalTT" implementationClass="org.ice1000.tt.editing.cubicaltt.CubicalTTHighlighterFactory"/>
 		<lang.refactoringSupport language="CubicalTT" implementationClass="org.ice1000.tt.editing.InplaceRenameRefactoringSupportProvider"/>
+		<lang.foldingBuilder language="CubicalTT" implementationClass="org.ice1000.tt.editing.cubicaltt.CubicalTTFoldingBuilder"/>
 		<colorSettingsPage implementation="org.ice1000.tt.editing.cubicaltt.CubicalTTColorSettingsPage"/>
 		<annotator language="CubicalTT" implementationClass="org.ice1000.tt.editing.cubicaltt.CubicalTTAnnotator"/>
 		<stubIndex implementation="org.ice1000.tt.psi.cubicaltt.CubicalTTModuleStubKey"/>
diff --git a/src/org/ice1000/tt/editing/cubicaltt/folding.kt b/src/org/ice1000/tt/editing/cubicaltt/folding.kt
new file mode 100644
index 0000000..ba2164f
--- /dev/null
+++ b/src/org/ice1000/tt/editing/cubicaltt/folding.kt
@@ -0,0 +1,75 @@
+package org.ice1000.tt.editing.cubicaltt
+
+import com.intellij.lang.ASTNode
+import com.intellij.lang.folding.FoldingBuilderEx
+import com.intellij.lang.folding.FoldingDescriptor
+import com.intellij.openapi.editor.Document
+import com.intellij.openapi.project.DumbAware
+import com.intellij.openapi.util.TextRange
+import com.intellij.psi.PsiComment
+import com.intellij.psi.PsiElement
+import com.intellij.psi.TokenType
+import org.ice1000.tt.FOLDING_PLACEHOLDER
+import org.ice1000.tt.editing.collectFoldRegions
+import org.ice1000.tt.psi.*
+import org.ice1000.tt.psi.cubicaltt.*
+
+class CubicalTTFoldingBuilder : FoldingBuilderEx(), DumbAware {
+	override fun getPlaceholderText(node: ASTNode) = when (node.elementType) {
+		CubicalTTTokenType.BLOCK_COMMENT -> "{---}"
+		CubicalTTTypes.SYSTEM -> "[$FOLDING_PLACEHOLDER]"
+		else -> FOLDING_PLACEHOLDER
+	}
+
+	override fun isCollapsedByDefault(node: ASTNode) = false
+
+	override fun buildFoldRegions(root: PsiElement, document: Document, quick: Boolean): Array<FoldingDescriptor> {
+		if (root !is CubicalTTFileImpl) return emptyArray()
+		return collectFoldRegions(root) { FoldingVisitor(it, document) }
+	}
+}
+
+private class FoldingVisitor(
+	private val descriptors: MutableList<FoldingDescriptor>,
+	private val document: Document
+) : CubicalTTVisitor() {
+	override fun visitData(o: CubicalTTData) {
+		val labels = o.labelList.takeIf { it.size > 1 } ?: return
+		descriptors += FoldingDescriptor(o, TextRange(labels.first().startOffset, labels.last().endOffset))
+	}
+
+	override fun visitSystem(o: CubicalTTSystem) {
+		val startLine = document.getLineNumber(o.startOffset)
+		val endLine = document.getLineNumber(o.endOffset)
+		if (startLine != endLine) descriptors.add(FoldingDescriptor(o, o.textRange))
+	}
+
+	override fun visitComment(comment: PsiComment?) {
+		if (comment?.elementType == CubicalTTTokenType.BLOCK_COMMENT)
+			descriptors += FoldingDescriptor(comment, comment.textRange)
+	}
+
+	override fun visitSplitBody(o: CubicalTTSplitBody) = layout(o)
+	override fun visitExpWhere(o: CubicalTTExpWhere) = layout(o)
+	override fun visitMutual(o: CubicalTTMutual) = layout(o)
+	override fun visitLetExp(o: CubicalTTLetExp) {
+		val layoutStart = o.childrenWithLeaves.firstOrNull { it.elementType == CubicalTTTypes.LAYOUT_START } ?: return
+		val layoutEnd = layoutStart.rightSiblings.firstOrNull {
+			it.elementType == CubicalTTTypes.KW_IN
+		}?.prevSiblingIgnoring<PsiElement>(TokenType.WHITE_SPACE) ?: return
+		descriptors += FoldingDescriptor(o, TextRange(layoutStart.startOffset, layoutEnd.endOffset))
+	}
+
+	private fun layout(o: PsiElement) {
+		val layoutStart = o.childrenWithLeaves.firstOrNull { it.elementType == CubicalTTTypes.LAYOUT_START } ?: return
+		val layoutEnd = layoutStart.rightSiblings.firstOrNull { it.elementType == CubicalTTTypes.LAYOUT_END } ?: o.lastChild
+		?: return
+		descriptors += FoldingDescriptor(o, TextRange(layoutStart.startOffset, layoutEnd.endOffset))
+	}
+
+	override fun visitModule(o: CubicalTTModule) {
+		val imports = o.importList.takeIf { it.size > 1 } ?: return
+		val startOffset = imports.first().moduleUsage?.startOffset ?: return
+		descriptors += FoldingDescriptor(o, TextRange(startOffset, imports.last().endOffset))
+	}
+}
diff --git a/src/org/ice1000/tt/editing/redprl/folding.kt b/src/org/ice1000/tt/editing/redprl/folding.kt
index 931aefe..2bedb39 100644
--- a/src/org/ice1000/tt/editing/redprl/folding.kt
+++ b/src/org/ice1000/tt/editing/redprl/folding.kt
@@ -37,7 +37,6 @@ private class FoldingVisitor(
 	private val document: Document
 ) : RedPrlVisitor() {
 
-
 	override fun visitComment(comment: PsiComment?) {
 		if (comment?.elementType == RedPrlTokenType.BLOCK_COMMENT)
 			descriptors += FoldingDescriptor(comment, comment.textRange)