diff --git a/libc/utils/LibcTableGenUtil/APIIndexer.cpp b/libc/utils/LibcTableGenUtil/APIIndexer.cpp
@@ -0,0 +1,154 @@
+
+#include "APIIndexer.h"
+
+#include "llvm/ADT/StringExtras.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/TableGen/Error.h"
+#include "llvm/TableGen/Record.h"
+
+namespace llvm_libc {
+
+static const char NamedTypeClassName[] = "NamedType";
+static const char PtrTypeClassName[] = "PtrType";
+static const char RestrictedPtrTypeClassName[] = "RestrictedPtrType";
+static const char ConstTypeClassName[] = "ConstType";
+static const char StructTypeClassName[] = "Struct";
+
+static const char StandardSpecClassName[] = "StandardSpec";
+static const char PublicAPIClassName[] = "PublicAPI";
+
+static bool isa(llvm::Record *Def, llvm::Record *TypeClass) {
+  llvm::RecordRecTy *RecordType = Def->getType();
+  llvm::ArrayRef<llvm::Record *> Classes = RecordType->getClasses();
+  // We want exact types. That is, we don't want the classes listed in
+  // spec.td to be subclassed. Hence, we do not want the record |Def|
+  // to be of more than one class type..
+  if (Classes.size() != 1)
+    return false;
+  return Classes[0] == TypeClass;
+}
+
+bool APIIndexer::isaNamedType(llvm::Record *Def) {
+  return isa(Def, NamedTypeClass);
+}
+
+bool APIIndexer::isaStructType(llvm::Record *Def) {
+  return isa(Def, StructClass);
+}
+
+bool APIIndexer::isaPtrType(llvm::Record *Def) {
+  return isa(Def, PtrTypeClass);
+}
+
+bool APIIndexer::isaConstType(llvm::Record *Def) {
+  return isa(Def, ConstTypeClass);
+}
+
+bool APIIndexer::isaRestrictedPtrType(llvm::Record *Def) {
+  return isa(Def, RestrictedPtrTypeClass);
+}
+
+bool APIIndexer::isaStandardSpec(llvm::Record *Def) {
+  return isa(Def, StandardSpecClass);
+}
+
+bool APIIndexer::isaPublicAPI(llvm::Record *Def) {
+  return isa(Def, PublicAPIClass);
+}
+
+std::string APIIndexer::getTypeAsString(llvm::Record *TypeRecord) {
+  if (isaNamedType(TypeRecord) || isaStructType(TypeRecord)) {
+    return std::string(TypeRecord->getValueAsString("Name"));
+  } else if (isaPtrType(TypeRecord)) {
+    return getTypeAsString(TypeRecord->getValueAsDef("PointeeType")) + " *";
+  } else if (isaConstType(TypeRecord)) {
+    return std::string("const ") +
+           getTypeAsString(TypeRecord->getValueAsDef("UnqualifiedType"));
+  } else if (isaRestrictedPtrType(TypeRecord)) {
+    return getTypeAsString(TypeRecord->getValueAsDef("PointeeType")) +
+           " *__restrict";
+  } else {
+    llvm::PrintFatalError(TypeRecord->getLoc(), "Invalid type.\n");
+  }
+}
+
+void APIIndexer::indexStandardSpecDef(llvm::Record *StandardSpec) {
+  auto HeaderSpecList = StandardSpec->getValueAsListOfDefs("Headers");
+  for (llvm::Record *HeaderSpec : HeaderSpecList) {
+    llvm::StringRef Header = HeaderSpec->getValueAsString("Name");
+    if (!StdHeader.hasValue() || Header == StdHeader) {
+      PublicHeaders.emplace(Header);
+      auto MacroSpecList = HeaderSpec->getValueAsListOfDefs("Macros");
+      // TODO: Trigger a fatal error on duplicate specs.
+      for (llvm::Record *MacroSpec : MacroSpecList)
+        MacroSpecMap[std::string(MacroSpec->getValueAsString("Name"))] =
+            MacroSpec;
+
+      auto TypeSpecList = HeaderSpec->getValueAsListOfDefs("Types");
+      for (llvm::Record *TypeSpec : TypeSpecList)
+        TypeSpecMap[std::string(TypeSpec->getValueAsString("Name"))] = TypeSpec;
+
+      auto FunctionSpecList = HeaderSpec->getValueAsListOfDefs("Functions");
+      for (llvm::Record *FunctionSpec : FunctionSpecList) {
+        FunctionSpecMap[std::string(FunctionSpec->getValueAsString("Name"))] =
+            FunctionSpec;
+      }
+
+      auto EnumerationSpecList =
+          HeaderSpec->getValueAsListOfDefs("Enumerations");
+      for (llvm::Record *EnumerationSpec : EnumerationSpecList) {
+        EnumerationSpecMap[std::string(
+            EnumerationSpec->getValueAsString("Name"))] = EnumerationSpec;
+      }
+    }
+  }
+}
+
+void APIIndexer::indexPublicAPIDef(llvm::Record *PublicAPI) {
+  // While indexing the public API, we do not check if any of the entities
+  // requested is from an included standard. Such a check is done while
+  // generating the API.
+  auto MacroDefList = PublicAPI->getValueAsListOfDefs("Macros");
+  for (llvm::Record *MacroDef : MacroDefList)
+    MacroDefsMap[std::string(MacroDef->getValueAsString("Name"))] = MacroDef;
+
+  auto TypeDeclList = PublicAPI->getValueAsListOfDefs("TypeDeclarations");
+  for (llvm::Record *TypeDecl : TypeDeclList)
+    TypeDeclsMap[std::string(TypeDecl->getValueAsString("Name"))] = TypeDecl;
+
+  auto StructList = PublicAPI->getValueAsListOfStrings("Structs");
+  for (llvm::StringRef StructName : StructList)
+    Structs.insert(std::string(StructName));
+
+  auto FunctionList = PublicAPI->getValueAsListOfStrings("Functions");
+  for (llvm::StringRef FunctionName : FunctionList)
+    Functions.insert(std::string(FunctionName));
+
+  auto EnumerationList = PublicAPI->getValueAsListOfStrings("Enumerations");
+  for (llvm::StringRef EnumerationName : EnumerationList)
+    Enumerations.insert(std::string(EnumerationName));
+}
+
+void APIIndexer::index(llvm::RecordKeeper &Records) {
+  NamedTypeClass = Records.getClass(NamedTypeClassName);
+  PtrTypeClass = Records.getClass(PtrTypeClassName);
+  RestrictedPtrTypeClass = Records.getClass(RestrictedPtrTypeClassName);
+  StructClass = Records.getClass(StructTypeClassName);
+  ConstTypeClass = Records.getClass(ConstTypeClassName);
+  StandardSpecClass = Records.getClass(StandardSpecClassName);
+  PublicAPIClass = Records.getClass(PublicAPIClassName);
+
+  const auto &DefsMap = Records.getDefs();
+  for (auto &Pair : DefsMap) {
+    llvm::Record *Def = Pair.second.get();
+    if (isaStandardSpec(Def))
+      indexStandardSpecDef(Def);
+    if (isaPublicAPI(Def)) {
+      if (!StdHeader.hasValue() ||
+          Def->getValueAsString("HeaderName") == StdHeader)
+        indexPublicAPIDef(Def);
+    }
+  }
+}
+
+} // namespace llvm_libc
diff --git a/libc/utils/LibcTableGenUtil/APIIndexer.h b/libc/utils/LibcTableGenUtil/APIIndexer.h
@@ -0,0 +1,66 @@
+
+#include "llvm/ADT/StringRef.h"
+#include "llvm/TableGen/Record.h"
+
+#include <string>
+#include <unordered_map>
+#include <unordered_set>
+
+namespace llvm_libc {
+
+class APIIndexer {
+private:
+  llvm::Optional<llvm::StringRef> StdHeader;
+
+  // TableGen classes in spec.td.
+  llvm::Record *NamedTypeClass;
+  llvm::Record *PtrTypeClass;
+  llvm::Record *RestrictedPtrTypeClass;
+  llvm::Record *ConstTypeClass;
+  llvm::Record *StructClass;
+  llvm::Record *StandardSpecClass;
+  llvm::Record *PublicAPIClass;
+
+  bool isaNamedType(llvm::Record *Def);
+  bool isaStructType(llvm::Record *Def);
+  bool isaPtrType(llvm::Record *Def);
+  bool isaConstType(llvm::Record *Def);
+  bool isaRestrictedPtrType(llvm::Record *Def);
+  bool isaStandardSpec(llvm::Record *Def);
+  bool isaPublicAPI(llvm::Record *Def);
+
+  void indexStandardSpecDef(llvm::Record *StandardSpec);
+  void indexPublicAPIDef(llvm::Record *PublicAPI);
+  void index(llvm::RecordKeeper &Records);
+
+public:
+  using NameToRecordMapping = std::unordered_map<std::string, llvm::Record *>;
+  using NameSet = std::unordered_set<std::string>;
+
+  // This indexes all headers, not just a specified one.
+  explicit APIIndexer(llvm::RecordKeeper &Records) : StdHeader(llvm::None) {
+    index(Records);
+  }
+
+  APIIndexer(llvm::StringRef Header, llvm::RecordKeeper &Records)
+      : StdHeader(Header) {
+    index(Records);
+  }
+
+  // Mapping from names to records defining them.
+  NameToRecordMapping MacroSpecMap;
+  NameToRecordMapping TypeSpecMap;
+  NameToRecordMapping EnumerationSpecMap;
+  NameToRecordMapping FunctionSpecMap;
+  NameToRecordMapping MacroDefsMap;
+  NameToRecordMapping TypeDeclsMap;
+
+  NameSet Structs;
+  NameSet Enumerations;
+  NameSet Functions;
+  NameSet PublicHeaders;
+
+  std::string getTypeAsString(llvm::Record *TypeRecord);
+};
+
+} // namespace llvm_libc
diff --git a/libc/utils/LibcTableGenUtil/CMakeLists.txt b/libc/utils/LibcTableGenUtil/CMakeLists.txt
@@ -0,0 +1,7 @@
+add_llvm_library(
+  LibcTableGenUtil
+  APIIndexer.cpp
+  APIIndexer.h
+  LINK_COMPONENTS Support
+)
+target_include_directories(LibcTableGenUtil PUBLIC ${LIBC_SOURCE_DIR})