diff --git a/editor/CMakeLists.txt b/editor/CMakeLists.txt
index be15bf5..4ab4120 100644
--- a/editor/CMakeLists.txt
+++ b/editor/CMakeLists.txt
@@ -29,3 +29,7 @@ target_include_directories(step4_test PRIVATE src)
 add_executable(step5_test tests/step5_test.cpp)
 target_include_directories(step5_test PRIVATE src)
 target_link_libraries(step5_test PRIVATE nlohmann_json::nlohmann_json)
+
+add_executable(step6_test tests/step6_test.cpp)
+target_include_directories(step6_test PRIVATE src)
+target_link_libraries(step6_test PRIVATE nlohmann_json::nlohmann_json)
diff --git a/editor/src/ast/Serialization.h b/editor/src/ast/Serialization.h
index fb197c3..d213270 100644
--- a/editor/src/ast/Serialization.h
+++ b/editor/src/ast/Serialization.h
@@ -136,3 +136,165 @@ inline json toJson(const ASTNode* node) {
 
     return j;
 }
+
+// --- Deserialization ---
+
+inline ASTNode* createNode(const std::string& conceptName) {
+    if (conceptName == "Module") return new Module();
+    if (conceptName == "Function") return new Function();
+    if (conceptName == "Variable") return new Variable();
+    if (conceptName == "Parameter") return new Parameter();
+    if (conceptName == "Block") return new Block();
+    if (conceptName == "Assignment") return new Assignment();
+    if (conceptName == "IfStatement") return new IfStatement();
+    if (conceptName == "WhileLoop") return new WhileLoop();
+    if (conceptName == "ForLoop") return new ForLoop();
+    if (conceptName == "Return") return new Return();
+    if (conceptName == "ExpressionStatement") return new ExpressionStatement();
+    if (conceptName == "BinaryOperation") return new BinaryOperation();
+    if (conceptName == "UnaryOperation") return new UnaryOperation();
+    if (conceptName == "FunctionCall") return new FunctionCall();
+    if (conceptName == "VariableReference") return new VariableReference();
+    if (conceptName == "IntegerLiteral") return new IntegerLiteral();
+    if (conceptName == "FloatLiteral") return new FloatLiteral();
+    if (conceptName == "StringLiteral") return new StringLiteral();
+    if (conceptName == "BooleanLiteral") return new BooleanLiteral();
+    if (conceptName == "NullLiteral") return new NullLiteral();
+    if (conceptName == "ListLiteral") return new ListLiteral();
+    if (conceptName == "IndexAccess") return new IndexAccess();
+    if (conceptName == "MemberAccess") return new MemberAccess();
+    if (conceptName == "PrimitiveType") return new PrimitiveType();
+    if (conceptName == "ListType") return new ListType();
+    if (conceptName == "SetType") return new SetType();
+    if (conceptName == "MapType") return new MapType();
+    if (conceptName == "TupleType") return new TupleType();
+    if (conceptName == "ArrayType") return new ArrayType();
+    if (conceptName == "OptionalType") return new OptionalType();
+    if (conceptName == "CustomType") return new CustomType();
+    if (conceptName == "DerefStrategy") return new DerefStrategy();
+    if (conceptName == "OptimizationLock") return new OptimizationLock();
+    if (conceptName == "LangSpecific") return new LangSpecific();
+    return nullptr;
+}
+
+inline void setPropertiesFromJson(ASTNode* node, const json& props) {
+    const auto& ct = node->conceptType;
+
+    if (ct == "Module") {
+        auto* n = static_cast<Module*>(node);
+        if (props.contains("name")) n->name = props["name"].get<std::string>();
+        if (props.contains("targetLanguage")) n->targetLanguage = props["targetLanguage"].get<std::string>();
+    }
+    else if (ct == "Function") {
+        auto* n = static_cast<Function*>(node);
+        if (props.contains("name")) n->name = props["name"].get<std::string>();
+    }
+    else if (ct == "Variable") {
+        auto* n = static_cast<Variable*>(node);
+        if (props.contains("name")) n->name = props["name"].get<std::string>();
+    }
+    else if (ct == "Parameter") {
+        auto* n = static_cast<Parameter*>(node);
+        if (props.contains("name")) n->name = props["name"].get<std::string>();
+    }
+    else if (ct == "ForLoop") {
+        auto* n = static_cast<ForLoop*>(node);
+        if (props.contains("iteratorName")) n->iteratorName = props["iteratorName"].get<std::string>();
+    }
+    else if (ct == "BinaryOperation") {
+        auto* n = static_cast<BinaryOperation*>(node);
+        if (props.contains("op")) n->op = props["op"].get<std::string>();
+    }
+    else if (ct == "UnaryOperation") {
+        auto* n = static_cast<UnaryOperation*>(node);
+        if (props.contains("op")) n->op = props["op"].get<std::string>();
+    }
+    else if (ct == "FunctionCall") {
+        auto* n = static_cast<FunctionCall*>(node);
+        if (props.contains("functionName")) n->functionName = props["functionName"].get<std::string>();
+    }
+    else if (ct == "VariableReference") {
+        auto* n = static_cast<VariableReference*>(node);
+        if (props.contains("variableName")) n->variableName = props["variableName"].get<std::string>();
+    }
+    else if (ct == "IntegerLiteral") {
+        auto* n = static_cast<IntegerLiteral*>(node);
+        if (props.contains("value")) n->value = props["value"].get<int>();
+    }
+    else if (ct == "FloatLiteral") {
+        auto* n = static_cast<FloatLiteral*>(node);
+        if (props.contains("value")) n->value = props["value"].get<std::string>();
+    }
+    else if (ct == "StringLiteral") {
+        auto* n = static_cast<StringLiteral*>(node);
+        if (props.contains("value")) n->value = props["value"].get<std::string>();
+    }
+    else if (ct == "BooleanLiteral") {
+        auto* n = static_cast<BooleanLiteral*>(node);
+        if (props.contains("value")) n->value = props["value"].get<bool>();
+    }
+    else if (ct == "MemberAccess") {
+        auto* n = static_cast<MemberAccess*>(node);
+        if (props.contains("memberName")) n->memberName = props["memberName"].get<std::string>();
+    }
+    else if (ct == "PrimitiveType") {
+        auto* n = static_cast<PrimitiveType*>(node);
+        if (props.contains("kind")) n->kind = props["kind"].get<std::string>();
+    }
+    else if (ct == "CustomType") {
+        auto* n = static_cast<CustomType*>(node);
+        if (props.contains("typeName")) n->typeName = props["typeName"].get<std::string>();
+    }
+    else if (ct == "DerefStrategy") {
+        auto* n = static_cast<DerefStrategy*>(node);
+        if (props.contains("strategy")) n->strategy = props["strategy"].get<std::string>();
+        if (props.contains("derefLocation")) n->derefLocation = props["derefLocation"].get<std::string>();
+        if (props.contains("owner")) n->owner = props["owner"].get<std::string>();
+    }
+    else if (ct == "OptimizationLock") {
+        auto* n = static_cast<OptimizationLock*>(node);
+        if (props.contains("lockedBy")) n->lockedBy = props["lockedBy"].get<std::string>();
+        if (props.contains("lockReason")) n->lockReason = props["lockReason"].get<std::string>();
+        if (props.contains("lockLevel")) n->lockLevel = props["lockLevel"].get<std::string>();
+        if (props.contains("affectedStrategies")) n->affectedStrategies = props["affectedStrategies"].get<std::string>();
+        if (props.contains("timestamp")) n->timestamp = props["timestamp"].get<std::string>();
+    }
+    else if (ct == "LangSpecific") {
+        auto* n = static_cast<LangSpecific*>(node);
+        if (props.contains("language")) n->language = props["language"].get<std::string>();
+        if (props.contains("idiomType")) n->idiomType = props["idiomType"].get<std::string>();
+        if (props.contains("rawSyntax")) n->rawSyntax = props["rawSyntax"].get<std::string>();
+        if (props.contains("semanticHint")) n->semanticHint = props["semanticHint"].get<std::string>();
+        if (props.contains("position")) n->position = props["position"].get<std::string>();
+    }
+}
+
+inline ASTNode* fromJson(const json& j) {
+    ASTNode* node = createNode(j["concept"].get<std::string>());
+    if (!node) return nullptr;
+
+    node->id = j["id"].get<std::string>();
+
+    if (j.contains("properties")) {
+        setPropertiesFromJson(node, j["properties"]);
+    }
+
+    if (j.contains("children")) {
+        for (auto& [role, arr] : j["children"].items()) {
+            for (auto& childJson : arr) {
+                ASTNode* child = fromJson(childJson);
+                if (child) node->addChild(role, child);
+            }
+        }
+    }
+
+    return node;
+}
+
+inline void deleteTree(ASTNode* node) {
+    if (!node) return;
+    for (auto* child : node->allChildren()) {
+        deleteTree(child);
+    }
+    delete node;
+}
diff --git a/editor/tests/step6_test.cpp b/editor/tests/step6_test.cpp
new file mode 100644
index 0000000..9e3853d
--- /dev/null
+++ b/editor/tests/step6_test.cpp
@@ -0,0 +1,127 @@
+// Step 6: JSON round-trip. Save Calculator → load → save again → compare (byte-identical).
+
+#include "../src/ast/Serialization.h"
+#include <cassert>
+#include <iostream>
+
+int main() {
+    // Build Calculator (same as step5)
+    Module calc("Calc_M001", "Calculator", "cpp");
+
+    Variable pi("Calc_V001", "PI");
+    PrimitiveType piType("Calc_VT001", "float");
+    pi.setChild("type", &piType);
+    calc.addChild("variables", &pi);
+
+    Function add("Calc_F001", "add");
+    PrimitiveType addRet("Calc_RT001", "int");
+    add.setChild("returnType", &addRet);
+
+    Parameter px("Calc_P001", "x");
+    PrimitiveType pxType("Calc_PT001", "int");
+    px.setChild("type", &pxType);
+    add.addChild("parameters", &px);
+
+    Parameter py("Calc_P002", "y");
+    PrimitiveType pyType("Calc_PT002", "int");
+    py.setChild("type", &pyType);
+    add.addChild("parameters", &py);
+
+    Assignment assign;
+    assign.id = "Calc_A001";
+    VariableReference assignTarget("c_VR_result", "result");
+    assign.setChild("target", &assignTarget);
+    BinaryOperation addOp("Calc_E001", "+");
+    VariableReference vrX("Calc_VR_x", "x");
+    VariableReference vrY("Calc_VR_y", "y");
+    addOp.setChild("left", &vrX);
+    addOp.setChild("right", &vrY);
+    assign.setChild("value", &addOp);
+    add.addChild("body", &assign);
+
+    Return addReturn;
+    addReturn.id = "Calc_R001";
+    VariableReference vrRetResult("c_VR_return", "result");
+    addReturn.setChild("value", &vrRetResult);
+    add.addChild("body", &addReturn);
+    calc.addChild("functions", &add);
+
+    Function multiply("Calc_F002", "multiply");
+    PrimitiveType mulRet("Calc_RT002", "int");
+    multiply.setChild("returnType", &mulRet);
+
+    Parameter pa("Calc_P003", "a");
+    PrimitiveType paType("Calc_PT003", "int");
+    pa.setChild("type", &paType);
+    multiply.addChild("parameters", &pa);
+
+    Parameter pb("Calc_P004", "b");
+    PrimitiveType pbType("Calc_PT004", "int");
+    pb.setChild("type", &pbType);
+    multiply.addChild("parameters", &pb);
+
+    Return mulReturn;
+    mulReturn.id = "Calc_R002";
+    BinaryOperation mulOp("Calc_E005", "*");
+    VariableReference vrA("Calc_VR_a", "a");
+    VariableReference vrB("Calc_VR_b", "b");
+    mulOp.setChild("left", &vrA);
+    mulOp.setChild("right", &vrB);
+    mulReturn.setChild("value", &mulOp);
+    multiply.addChild("body", &mulReturn);
+    calc.addChild("functions", &multiply);
+
+    // --- Round-trip ---
+
+    // Save 1
+    json j1 = toJson(&calc);
+    std::string s1 = j1.dump(2);
+
+    // Load
+    ASTNode* loaded = fromJson(j1);
+    assert(loaded != nullptr);
+
+    // Verify loaded tree structure
+    assert(loaded->conceptType == "Module");
+    auto* lm = static_cast<Module*>(loaded);
+    assert(lm->name == "Calculator");
+    assert(lm->targetLanguage == "cpp");
+    assert(lm->getChildren("functions").size() == 2);
+    assert(lm->getChildren("variables").size() == 1);
+
+    // Verify deep node
+    auto* lf = static_cast<Function*>(lm->getChildren("functions")[0]);
+    assert(lf->name == "add");
+    assert(lf->parent == loaded);
+    assert(lf->getChildren("parameters").size() == 2);
+    assert(lf->getChildren("body").size() == 2);
+
+    auto* lp = static_cast<Parameter*>(lf->getChildren("parameters")[0]);
+    assert(lp->name == "x");
+    assert(lp->parent == lf);
+    auto* lpt = static_cast<PrimitiveType*>(lp->getChild("type"));
+    assert(lpt->kind == "int");
+    assert(lpt->parent == lp);
+
+    auto* la = static_cast<Assignment*>(lf->getChildren("body")[0]);
+    auto* lbo = static_cast<BinaryOperation*>(la->getChild("value"));
+    assert(lbo->op == "+");
+    assert(static_cast<VariableReference*>(lbo->getChild("left"))->variableName == "x");
+
+    // Save 2
+    json j2 = toJson(loaded);
+    std::string s2 = j2.dump(2);
+
+    // Compare: must be byte-identical
+    if (s1 != s2) {
+        std::cerr << "MISMATCH!\n--- Save 1 ---\n" << s1
+                  << "\n--- Save 2 ---\n" << s2 << std::endl;
+        assert(false && "Round-trip JSON not identical");
+    }
+
+    // Cleanup heap-allocated tree
+    deleteTree(loaded);
+
+    std::cout << "Step 6: PASS — JSON round-trip (save/load/save identical)" << std::endl;
+    return 0;
+}