diff --git a/Meta/Lagom/Tools/CodeGenerators/JSSpecCompiler/AST/AST.h b/Meta/Lagom/Tools/CodeGenerators/JSSpecCompiler/AST/AST.h
new file mode 100644
index 0000000000..77df78963f
--- /dev/null
+++ b/Meta/Lagom/Tools/CodeGenerators/JSSpecCompiler/AST/AST.h
@@ -0,0 +1,338 @@
+/*
+ * Copyright (c) 2023, Dan Klishch <danilklishch@gmail.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/RefCounted.h>
+#include <AK/RefPtr.h>
+#include <AK/Vector.h>
+
+#include "Forward.h"
+
+namespace JSSpecCompiler {
+
+template<typename T>
+RefPtr<T> as(NullableTree const& tree)
+{
+    return dynamic_cast<T*>(tree.ptr());
+}
+
+// ===== Generic nodes =====
+class Node : public RefCounted<Node> {
+public:
+    virtual ~Node() = default;
+
+    void format_tree(StringBuilder& builder);
+
+    virtual bool is_type() { return false; }
+
+protected:
+    template<typename... Parameters>
+    void dump_node(StringBuilder& builder, AK::CheckedFormatString<Parameters...>&& fmtstr, Parameters const&... parameters);
+
+    virtual void dump_tree(StringBuilder& builder) = 0;
+};
+
+class ErrorNode : public Node {
+public:
+    ErrorNode() { }
+
+protected:
+    void dump_tree(StringBuilder& builder) override;
+};
+
+inline Tree const error_tree = make_ref_counted<ErrorNode>();
+
+// ===== Concrete evaluatable nodes =====
+class MathematicalConstant : public Node {
+public:
+    MathematicalConstant(i64 number)
+        : m_number(number)
+    {
+    }
+
+    // TODO: This should be able to hold arbitrary number
+    i64 m_number;
+
+protected:
+    void dump_tree(StringBuilder& builder) override;
+};
+
+class StringLiteral : public Node {
+public:
+    StringLiteral(StringView literal)
+        : m_literal(literal)
+    {
+    }
+
+    StringView m_literal;
+
+protected:
+    void dump_tree(StringBuilder& builder) override;
+};
+
+#define ENUMERATE_UNARY_OPERATORS(F) \
+    F(Invalid)                       \
+    F(Minus)                         \
+    F(AssertCompletion)
+
+#define ENUMERATE_BINARY_OPERATORS(F) \
+    F(Invalid)                        \
+    F(CompareLess)                    \
+    F(CompareGreater)                 \
+    F(CompareNotEqual)                \
+    F(CompareEqual)                   \
+    F(Assignment)                     \
+    F(Declaration)                    \
+    F(Plus)                           \
+    F(Minus)                          \
+    F(Multiplication)                 \
+    F(Division)                       \
+    F(Comma)                          \
+    F(MemberAccess)                   \
+    F(FunctionCall)                   \
+    F(ArraySubscript)
+
+#define NAME(name) name,
+#define STRINGIFY(name) #name##sv,
+
+enum class UnaryOperator {
+    ENUMERATE_UNARY_OPERATORS(NAME)
+};
+
+inline constexpr StringView unary_operator_names[] = {
+    ENUMERATE_UNARY_OPERATORS(STRINGIFY)
+};
+
+enum class BinaryOperator {
+#define NAME(name) name,
+    ENUMERATE_BINARY_OPERATORS(NAME)
+};
+
+inline constexpr StringView binary_operator_names[] = {
+    ENUMERATE_BINARY_OPERATORS(STRINGIFY)
+};
+
+#undef NAME
+#undef STRINGIFY
+
+class BinaryOperation : public Node {
+public:
+    BinaryOperation(BinaryOperator operation, Tree left, Tree right)
+        : m_operation(operation)
+        , m_left(left)
+        , m_right(right)
+    {
+    }
+
+    BinaryOperator m_operation;
+    Tree m_left;
+    Tree m_right;
+
+protected:
+    void dump_tree(StringBuilder& builder) override;
+};
+
+class UnaryOperation : public Node {
+public:
+    UnaryOperation(UnaryOperator operation, Tree operand)
+        : m_operation(operation)
+        , m_operand(operand)
+    {
+    }
+
+    UnaryOperator m_operation;
+    Tree m_operand;
+
+protected:
+    void dump_tree(StringBuilder& builder) override;
+};
+
+class IsOneOfOperation : public Node {
+public:
+    IsOneOfOperation(Tree operand, Vector<Tree>&& compare_values)
+        : m_operand(operand)
+        , m_compare_values(move(compare_values))
+    {
+    }
+
+    Tree m_operand;
+    Vector<Tree> m_compare_values;
+
+protected:
+    void dump_tree(StringBuilder& builder) override;
+};
+
+class UnresolvedReference : public Node {
+public:
+    UnresolvedReference(StringView name)
+        : m_name(name)
+    {
+    }
+
+    StringView m_name;
+
+protected:
+    void dump_tree(StringBuilder& builder) override;
+};
+
+class ReturnExpression : public Node {
+public:
+    ReturnExpression(Tree return_value)
+        : m_return_value(return_value)
+    {
+    }
+
+    Tree m_return_value;
+
+protected:
+    void dump_tree(StringBuilder& builder) override;
+};
+
+class AssertExpression : public Node {
+public:
+    AssertExpression(Tree condition)
+        : m_condition(condition)
+    {
+    }
+
+    Tree m_condition;
+
+protected:
+    void dump_tree(StringBuilder& builder) override;
+};
+
+class IfBranch : public Node {
+public:
+    IfBranch(Tree condition, Tree branch)
+        : m_condition(condition)
+        , m_branch(branch)
+    {
+    }
+
+    Tree m_condition;
+    Tree m_branch;
+
+protected:
+    void dump_tree(StringBuilder& builder) override;
+};
+
+class ElseIfBranch : public Node {
+public:
+    ElseIfBranch(Optional<Tree> condition, Tree branch)
+        : m_condition(condition)
+        , m_branch(branch)
+    {
+    }
+
+    Optional<Tree> m_condition;
+    Tree m_branch;
+
+protected:
+    void dump_tree(StringBuilder& builder) override;
+};
+
+class TreeList : public Node {
+public:
+    TreeList(Vector<Tree>&& expressions_)
+        : m_expressions(move(expressions_))
+    {
+    }
+
+    Vector<Tree> m_expressions;
+
+protected:
+    void dump_tree(StringBuilder& builder) override;
+};
+
+class RecordDirectListInitialization : public Node {
+public:
+    struct Argument {
+        Tree name;
+        Tree value;
+    };
+
+    RecordDirectListInitialization(Tree type_reference, Vector<Argument>&& arguments)
+        : m_type_reference(type_reference)
+        , m_arguments(move(arguments))
+    {
+    }
+
+    Tree m_type_reference;
+    Vector<Argument> m_arguments;
+
+protected:
+    void dump_tree(StringBuilder& builder) override;
+};
+
+class FunctionCall : public Node {
+public:
+    FunctionCall(Tree name, Vector<Tree>&& arguments)
+        : m_name(name)
+        , m_arguments(move(arguments))
+    {
+    }
+
+    Tree m_name;
+    Vector<Tree> m_arguments;
+
+protected:
+    void dump_tree(StringBuilder& builder) override;
+};
+
+class SlotName : public Node {
+public:
+    SlotName(StringView member_name)
+        : m_member_name(member_name)
+    {
+    }
+
+    StringView m_member_name;
+
+protected:
+    void dump_tree(StringBuilder& builder) override;
+};
+
+class Variable : public Node {
+public:
+    Variable(StringView variable_name)
+        : m_name(variable_name)
+    {
+    }
+
+    StringView m_name;
+
+protected:
+    void dump_tree(StringBuilder& builder) override;
+};
+
+class FunctionPointer : public Node {
+public:
+    FunctionPointer(StringView function_name)
+        : m_function_name(function_name)
+    {
+    }
+
+    StringView m_function_name;
+
+protected:
+    void dump_tree(StringBuilder& builder) override;
+};
+
+}
+
+namespace AK {
+
+template<>
+struct Formatter<JSSpecCompiler::Tree> : Formatter<StringView> {
+    ErrorOr<void> format(FormatBuilder& builder, JSSpecCompiler::Tree const& tree)
+    {
+        tree->format_tree(builder.builder());
+        return {};
+    }
+};
+
+}
diff --git a/Meta/Lagom/Tools/CodeGenerators/JSSpecCompiler/AST/ASTPrinting.cpp b/Meta/Lagom/Tools/CodeGenerators/JSSpecCompiler/AST/ASTPrinting.cpp
new file mode 100644
index 0000000000..32dd6a1c8e
--- /dev/null
+++ b/Meta/Lagom/Tools/CodeGenerators/JSSpecCompiler/AST/ASTPrinting.cpp
@@ -0,0 +1,137 @@
+/*
+ * Copyright (c) 2023, Dan Klishch <danilklishch@gmail.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/StringBuilder.h>
+#include <AK/TemporaryChange.h>
+
+#include "AST/AST.h"
+
+namespace JSSpecCompiler {
+
+void Node::format_tree(StringBuilder& builder)
+{
+    static int current_depth = -1;
+    TemporaryChange<int> depth_change(current_depth, current_depth + 1);
+    builder.append_repeated(' ', current_depth * 2);
+    dump_tree(builder);
+}
+
+template<typename... Parameters>
+void Node::dump_node(StringBuilder& builder, AK::CheckedFormatString<Parameters...>&& fmtstr, Parameters const&... parameters)
+{
+    builder.append("<"sv);
+    AK::VariadicFormatParams<AK::AllowDebugOnlyFormatters::No, Parameters...> variadic_format_params { parameters... };
+    MUST(AK::vformat(builder, fmtstr.view(), variadic_format_params));
+    builder.append(">\n"sv);
+}
+
+void ErrorNode::dump_tree(StringBuilder& builder)
+{
+    dump_node(builder, "Error");
+}
+
+void MathematicalConstant::dump_tree(StringBuilder& builder)
+{
+    dump_node(builder, "MathematicalConstant {}", m_number);
+}
+
+void StringLiteral::dump_tree(StringBuilder& builder)
+{
+    dump_node(builder, "StringLiteral {}", m_literal);
+}
+
+void BinaryOperation::dump_tree(StringBuilder& builder)
+{
+    dump_node(builder, "BinaryOperation {}", binary_operator_names[to_underlying(m_operation)]);
+    m_left->format_tree(builder);
+    m_right->format_tree(builder);
+}
+
+void UnaryOperation::dump_tree(StringBuilder& builder)
+{
+    dump_node(builder, "UnaryOperation {}", unary_operator_names[to_underlying(m_operation)]);
+    m_operand->format_tree(builder);
+}
+
+void IsOneOfOperation::dump_tree(StringBuilder& builder)
+{
+    dump_node(builder, "IsOneOf");
+    m_operand->format_tree(builder);
+    for (auto const& compare_value : m_compare_values)
+        compare_value->format_tree(builder);
+}
+
+void UnresolvedReference::dump_tree(StringBuilder& builder)
+{
+    dump_node(builder, "UnresolvedReference {}", m_name);
+}
+
+void ReturnExpression::dump_tree(StringBuilder& builder)
+{
+    dump_node(builder, "ReturnExpression");
+    m_return_value->format_tree(builder);
+}
+
+void AssertExpression::dump_tree(StringBuilder& builder)
+{
+    dump_node(builder, "AssertExpression");
+    m_condition->format_tree(builder);
+}
+
+void IfBranch::dump_tree(StringBuilder& builder)
+{
+    dump_node(builder, "IfBranch");
+    m_condition->format_tree(builder);
+    m_branch->format_tree(builder);
+}
+
+void ElseIfBranch::dump_tree(StringBuilder& builder)
+{
+    dump_node(builder, "ElseIfBranch {}", m_condition.has_value() ? "ElseIf" : "Else");
+    if (m_condition.has_value())
+        (*m_condition)->format_tree(builder);
+    m_branch->format_tree(builder);
+}
+
+void TreeList::dump_tree(StringBuilder& builder)
+{
+    dump_node(builder, "TreeList");
+    for (auto const& expression : m_expressions)
+        expression->format_tree(builder);
+}
+
+void RecordDirectListInitialization::dump_tree(StringBuilder& builder)
+{
+    dump_node(builder, "RecordDirectListInitialization");
+    m_type_reference->format_tree(builder);
+    for (auto const& argument : m_arguments)
+        builder.appendff("{}{}", argument.name, argument.value);
+}
+
+void FunctionCall::dump_tree(StringBuilder& builder)
+{
+    dump_node(builder, "FunctionCall");
+    m_name->format_tree(builder);
+    for (auto const& argument : m_arguments)
+        argument->format_tree(builder);
+}
+
+void SlotName::dump_tree(StringBuilder& builder)
+{
+    dump_node(builder, "Slot {}", m_member_name);
+}
+
+void Variable::dump_tree(StringBuilder& builder)
+{
+    dump_node(builder, "Var {}", m_name);
+}
+
+void FunctionPointer::dump_tree(StringBuilder& builder)
+{
+    dump_node(builder, "Func {}", m_function_name);
+}
+
+}
diff --git a/Meta/Lagom/Tools/CodeGenerators/JSSpecCompiler/Forward.h b/Meta/Lagom/Tools/CodeGenerators/JSSpecCompiler/Forward.h
new file mode 100644
index 0000000000..50da4f2b1c
--- /dev/null
+++ b/Meta/Lagom/Tools/CodeGenerators/JSSpecCompiler/Forward.h
@@ -0,0 +1,39 @@
+/*
+ * Copyright (c) 2023, Dan Klishch <danilklishch@gmail.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Forward.h>
+
+namespace JSSpecCompiler {
+
+// AST/AST.h
+class NodeSubtreePointer;
+
+class Node;
+using NullableTree = RefPtr<Node>;
+using Tree = NonnullRefPtr<Node>;
+class ErrorNode;
+
+class ScopedBlock;
+class MathematicalConstant;
+class StringLiteral;
+class BinaryOperation;
+class UnaryOperation;
+class IsOneOfOperation;
+class UnresolvedReference;
+class ReturnExpression;
+class AssertExpression;
+class IfBranch;
+class ElseIfBranch;
+class TreeList;
+class RecordDirectListInitialization;
+class FunctionCall;
+class SlotName;
+class Variable;
+class FunctionPointer;
+
+}