diff --git a/libc/utils/HdrGen/PublicAPICommand.h b/libc/utils/HdrGen/PublicAPICommand.h
@@ -36,6 +36,61 @@ class PublicAPICommand : public Command {
            const Command::ErrorReporter &Reporter) const override;
 };
 
+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
 
 #endif // LLVM_LIBC_UTILS_HDRGEN_PUBLICAPICOMMAND_H